Isn’t it surprising that scientists have a better

understanding of how many stars there are in the galaxy than how many species there are on Earth？ Their estimates of global species diversity vary from 2 to 100 million species. Most people agree on an estimate of somewhere near 10 million and yet only 1.75 million have actually been named. Current knowledge of species diversity is limited. This problem becomes more serious because there is a lack of a central database or list of the world’s species.

New species are still being discovered — even new birds and mammals(哺乳动物). On average, about three new species of birds are found each year, and since 1990, 10 new species of monkeys have been discovered. Other groups are still far from being completely described: an estimated 40 percent of freshwater fishes in South America have not yet been classified.

Scientists were startled in 1980 by the discovery of a huge diversity of insects in tropical forests. In one study of just 19 trees in Panama, 960 new species of beetles were discovered.

As scientists begin investigating other little-known ecosystem, like the soil and the deep sea, “surprising” discoveries of species become commonplace. There is nothing strange about this, though, since as many as a million undescribed species are believed to live in the deep sea. And one gram of a small-sized piece of land might hold 90 million bacteria(菌类) and other microbes(微生物). How many species these communities contain is still anyone’s guess.

16. Which of the following is true？

A) Scientists have a sound knowledge about the diversity of species

B) Scientists don’t know much about the number of stars in the galaxy

C) Scientists show more interest in stars in the galaxy than in species on Earth

D) Scientists don’t agree on the number of species in the world

17. How many species are there on Earth according to most scientists？

A) About 2 million

B) About 10 million

C) About 100 million

D) About 1.75 million

18. In which of the following groups is the discovery of new species not mentioned in

the passage？

A) Birds

B) Monkeys

C) Trees

D) Freshwater fish

19. What can you learn from the passage？

A) The soil and the deep sea belong to communities that haven’t been fully explored

B) It is surprising news wherever new species are discovered in the deep sea

C) About 90 million species are believed to live in the deep sea

D) A million species in the deep sea have been discovered and named

20. Which of the following best reveals the main idea of the passage？

A) Surprising discoveries of new species are commonplace

B) The mystery of the deep sea and the soil remains to be uncovered

C) Knowledge of global species diversity is still limited

D) Estimates of global species diversity vary among scientists