文档介绍：Part II Cloze (10 points)
Directions: There are 20 blanks in the following passage. For each blank are four choices marked A, B, C and D. You should choose the one that best fits in to the passage. Then mark the corresponding letter with a single line through the center.
Scientists searching for precious metals have turned to the ocean floor, where natural chimneys are spewing out (地面天然裂口不断喷出) a metal-enriched black dust containing particles of gold, silver and zinc.
Scientists 16 A these hot springs are recreating the process which, billions of years ago, created 17 C metal deposits now found on land.
The discovery is giving geologists a 18B D into the earth’s early history and fueling some new theories on origin of life.
It also has huge implications for 19 panies.
Geologists are just beginning to understand how these chimneys, 20CA , clusters of sulfur and minerals (硫和其它矿物的聚集物), are formed, and what makes them spew out the mineralized dust.
At present it is mercially 21A D for panies to operate beneath the sea, although some scientists believe the “black smokers”, 22B A known as active mineralizing systems, will be a major -- and renewable -- source of metals in the next decade.
23A C the meantime, panies are using the ocean-floor research to locate similar deposits on land.
“The hottest thing in the mining research game right now is the 24 B 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 geologist.
Canada has mined some of the richest copper, zinc and gold 25 B in the world. In the past year, panies have used knowledge about where mineral formations 26AC on the ocean floor to find the deposits on land.
Geologists are excited because, 27 A metal deposits on land, which are tow or three billion years old, the undersea deposits keep 28B themselves.
“It’s really incredible to think that that we have a renewable metal resource 29D we’ve been taught to th