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Scientists searching for precious metals have turned to the ocean floor, where natural chimneys are spewing out a metal-enriched black dust containing particles of gold, silver and zinc.
Scientists 31 these hot springs are recreating the process which, billions of years ago, created 32 metal deposits now found on land.
The discovery is giving geologists a 33 into the earth’s early history and fuelling some new theories on origin of life.
It also has huge implications for 34 companies.
Geologists are just beginning to understand how these chimneys, 35 clusters of sulphur and minerals, are formed, and what makes them spew out the mineralized dust.
At present it is not commercially 36 for mining companies to operate beneath the sea, although some scientists believe the “black smokers”, 37 known as active mineralizing systems, will be a major—and renewable—source of metals in the next decade.
38 the meantime, mining companies are using the ocean-floor research to locate similar deposits on land.
“The hottest thing in the mining research game right now is the 39 within the past few years of mineral deposits currently forming—in front of our eyes—on the ocean floor,” said Dr. Joseph Fox, a Montreal (加拿大蒙特利尔) geologist.
Canada has mined some of the richest copper, zinc and gold 40 in the world. In the past year, mining companies have used knowledge about where mineral formations 41 on the ocean floor to find the deposits on land.
Geologists are excited because, 42 metal deposits on land, which are two or three billion years old, the undersea deposits keep 43 themselves.
“It’s really incredible to think that we have a renewable metal resource 44 we’ve been taught to think of metal resources as non-renewable,” Fox said.
The 30-foot-high (10-metre) chimneys or vents, 45 in 1979, are found along fractures in the ocean’s crust.
Scientists believe the deposits form when cold sea-water seeps into the fractures, leaving metals 46 it is drawn down.
As the water travels in the direction of the earth’s core, it 47 up. Eventually, the hot water rises, carrying with it the hot metal sulphide 48 the ocean floor.
When the hot sulphide meets the cold sea water, a thick black smoke-like substance is formed, spewing out of vents in built-up deposits of 49 .
The particles in the smoke eventually 50 on the ocean floor, forming vast solid sheets of metal sulphide.
31. A. believe B. thought C. uncover D. found
32. A. smooth B. tiny C. vast D. rust
33. A. chance B. revision C. weapon D. glimpse
34. A. metal B. mining C. alloy D. global
35. A. made of B. consisting in C. resulted from D. dealing with
36. A. periodic B. reliable C. comparative D. feasible
37. A. formally B. chiefly C. economically D. occasionally
38. A. At B. On C. In D. For
39. A. invention B. discovery C. findings D. theory
40. A. samples B. deposits C. mines D. fractions
41. A. range B. suffer C. occur D. form
42. A. unlike B. like C. as D. except
43. A. to renew B. renewing C. having renewed D. to be renewed
44. A. before B. until C. because D. when
45. A. broken B. fixed C. discovered D. originated
46. A. since B. as C. for D. whereas
47. A. speeds B. goes C. gives D. heats
48. A. from B. on C. toward D. beyond
49. A. sulphide B. substance C. deposits D. element
50. A. rely B. move C. turn D. settle