『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 18 Passage 3阅读练习：Look at the four squares  that indicate where the following sentence could be added to the passage. The descending stream of electrons divides at the point where the new positive-stream channel intersects the established path.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.真题题目及答案解析，TPO/Official 18 Passage 3阅读原文范文音频翻译

托福TPO/Official 18 Passage 3阅读原文Look at the four squares  that indicate where the following sentence could be added to the passage. The descending stream of electrons divides at the point where the new positive-stream channel intersects the established path.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.题目答案及解析-新东方托福官方网校手机版

闪电是由暴风云的放电所产生的明亮闪光。

Lightning is a brilliant flash of light produced by an electrical discharge from a storm cloud.

当一个带负电荷的粒子区域和一个带正电荷的粒子区域之间的吸引力变得如此之大，以致于带电粒子突然冲到一起时，就会发生放电。

The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenly rush together.

相反的带电粒子聚集在一起，抵消了电的张力，释放出大量的能量，我们称之为闪电。

The coming together of the oppositely charged particles neutralizes the electrical tension and releases a tremendous amount of energy, which we see as lightning.

带正电荷和负电荷的粒子在风暴云的发展过程中发生分离。

The separation of positively and negatively charged particles takes place during the development of the storm cloud.

在风暴云中形成的带电粒子的分离具有三明治状的结构。

The separation of charged particles that forms in a storm cloud has a sandwich-like structure.

带正电荷的粒子集中在云团的顶部和底部，但中间区域带负电荷。

Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged.

最近在该领域进行的测量和实验室模拟为带电粒子的结构如何形成提供了一个有希望的解释。

Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms.

所发生的是小的（毫米到厘米大小）冰球在云的寒冷上部区域形成。

What happens is that small (millimeter- to centimeter-size) pellets of ice form in the cold upper regions of the cloud.

当这些冰粒下落时，其中一些会撞击云团中心更小的冰晶。

When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud.

云层中心的温度在零下15摄氏度或以下。

The temperature at the center of the cloud is about -15˚C or lower.

在这样的温度下，冰球和冰晶的碰撞会导致电荷转移，从而冰球带上负电荷，冰晶带上正电荷。

At such temperatures, the collision between the ice pellets and the ice crystals causes electrical charges to shift so that the ice pellets acquire a negative charge and the ice crystals become positively charged.

然后上升气流将带正电的冰晶带到云的顶部。

Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud.

较重的带负电荷的冰球被集中在中心。

The heavier, negatively charged ice pellets are left to concentrate in the center.

这个过程解释了为什么云的顶部带正电，而中心带负电。

This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged.

带负电荷的区域很大：几百米厚，直径几公里。

The negatively charged region is large: several hundred meters thick and several kilometers in diameter.

在这个巨大的、寒冷的、带负电荷的区域下方，云团温度高于零下15度。在这样的温度下，冰晶和下落的冰粒发生碰撞，产生带正电荷的冰粒，然后在云团底部形成一个小区域。

Below this large, cold, negatively charged region, the cloud is warmer than -15˚C, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud.

当云中电荷分离崩溃时，大多数闪电发生在云中。

Most lightning takes place within a cloud when the charge separation within the cloud collapses.

然而，随着风暴云的发展，云层下的地面会带上正电荷，闪电会在云层的负电荷和正电荷地面之间以放电的形式发生。

However, as the storm cloud develops, the ground beneath the cloud becomes positively charged and lightning can take place in the form of an electrical discharge between the negative charge of the cloud and the positively charged ground.

击中地面的闪电最有可能是破坏性的，所以尽管它只占所有闪电的20%，但它已经得到了许多科学关注。

Lightning that strikes the ground is the most likely to be destructive, so even though it represents only 20 percent of all lightning, it has received a lot of scientific attention.

利用高速摄影技术，科学家们已经确定从云层到地面的闪电发生有两个步骤。

Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground.

首先，形成连接云和地面的通道或路径。

First, a channel, or path, is formed that connects the cloud and the ground.

然后，一股强大的电子流沿着这条路径从云层到达地面，就像我们看到的闪电一样，正是这股电流照亮了通道。

Then a strong current of electrons follows that path from the cloud to the ground, and it is that current that illuminates the channel as the lightning we see.

当电子从云层底部涌向地面时，通道的形成就开始了。

The formation of the channel is initiated when electrons surge from the cloud base toward the ground.

当这些带负电荷的电子流到达距离地面100米以内的地方时，就会遇到一股来自地面的带正电荷的粒子流。

When a stream of these negatively charged electrons comes within 100 meters of the ground, it is met by a stream of positively charged particles that comes up from the ground.

当带正电和负电的气流相遇时，一个完整的连接云和地面的通道就形成了。

When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed.

这个通道的直径只有几厘米，但它的宽度足以让电子以闪电的形式跟随通道到达地面。

The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning.

与电子云中的电子波相遇的正粒子流通常来自于一个高而尖的结构，如金属旗杆或塔。

The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall, pointed structure such as a metal flagpole or a tower.

这就是为什么在穿过完整的通道之后的闪电经常击中一个高层建筑的原因。

That is why the subsequent lightning that follows the completed channel often strikes a tall structure.

一旦形成了通道，通常会有几次闪电放电，每次放电都是由电子流和沿着既定路径的正粒子流相遇形成的。

Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path.

然而，有时，沿着已建立的通道的电子流会遇到正的电子流，正的电子流从地面开始形成新的路径。

Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground.

结果是一个分叉的闪电击中地面的两个地方。

The result is a forked lightning that strikes the ground in two places.

According to paragraph 1, all of the following take place in the development of a flash of lightning EXCEPT

According to paragraph 2, what causes ice crystals to become positively charged?

According to paragraph 2, why are positively charged ice pellets produced in the lower part of the cloud?

According to paragraph 2, the middle region of a cloud becomes negatively charged due to all of the following EXCEPT

The author remarks that “Lightning that strikes the ground is the most likely to be destructive” in order to explain why

The word “illuminates” in the passage is closest in meaning to

Which of the following claims about lightning strikes can be inferred from paragraph 5?

It can be inferred from paragraph 2 that part of the reason that the top of a storm cloud becomes positively charged is that

Look at the four squares  that indicate where the following sentence could be added to the passage. The descending stream of electrons divides at the point where the new positive-stream channel intersects the established path.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Lightning Lightning is a brilliant flash of light produced by an electrical discharge from a storm cloud. The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenly rush together. The coming together of the oppositely charged particles neutralizes the electrical tension and releases a tremendous amount of energy, which we see as lightning. The separation of positively and negatively charged particles takes place during the development of the storm cloud. The separation of charged particles that forms in a storm cloud has a sandwich-like structure. Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged. Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms. What happens is that small (millimeter- to centimeter-size) pellets of ice form in the cold upper regions of the cloud. When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud. The temperature at the center of the cloud is about -15˚C or lower. At such temperatures, the collision between the ice pellets and the ice crystals causes electrical charges to shift so that the ice pellets acquire a negative charge and the ice crystals become positively charged. Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud. The heavier, negatively charged ice pellets are left to concentrate in the center. This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged. The negatively charged region is large: several hundred meters thick and several kilometers in diameter. Below this large, cold, negatively charged region, the cloud is warmer than -15˚C, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud. Most lightning takes place within a cloud when the charge separation within the cloud collapses. However, as the storm cloud develops, the ground beneath the cloud becomes positively charged and lightning can take place in the form of an electrical discharge between the negative charge of the cloud and the positively charged ground. Lightning that strikes the ground is the most likely to be destructive, so even though it represents only 20 percent of all lightning, it has received a lot of scientific attention. Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground. First, a channel, or path, is formed that connects the cloud and the ground. Then a strong current of electrons follows that path from the cloud to the ground, and it is that current that illuminates the channel as the lightning we see. The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground, it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall, pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure.   Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path.  Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground.  The result is a forked lightning that strikes the ground in two places.