2018考博英语必会语法知识点：现在完成时
2018考博英语复习初期，夯实基础是首要任务，作为英语最基础的知识就是语法，新东方在线考博英语频道整理了一系列考博英语必会语法知识点供考生们参考复习。
现在完成时用来表示之前已发生或完成的动作或状 态，其结果的确和现在有联系。动作或状态发生在过去 但它的影响现在还存在;也可表示持续到现在的动作或 状态。其构成： have (has) +过去分词。
用于现在完成时的句型
1)It is the first / second time…. that…结构中的从句部分，用现在完成时。
It is the first time that I have visited the city.
It was the third time that the boy had been late.
2)This is the… that…结构，that 从句要用现在完成时.
This is the best film that I've (ever) seen.
这是我看过的最好的电影。
This is the first time (that) I've heard him sing. 这是我第一次听他唱歌。
典型例题
(1) ---Do you know our town at all?
---No, this is the first time I ___ here.
A. was B. have been C. came D. am coming
答案B. This is the first time 后面所加从句应为现在完成时，故选B。
(2) ---Have you ____ been to our town before?
---No, it's the first time I ___ here.
A. even, come B. even, have come C. ever, come D. ever, have come
答案D. ever意为曾经或无论何时，反意词为never，此两词常用于完成时。 This is the largest fish I have ever seen. It is / was the first time +that-clause 的句型中，从句要用完成时。
注意：非延续性动词的否定形式可以与表示延续时间的状语连用。即动作不发生的状态是可以持续的。
(错)I have received his letter for a month.
(对)I haven't received his letter for almost a month.