蔣玉蓮

The sixth mass extinction is not a worry for the future. Its happening now，much faster than previously expected， and its entirely our fault， according to a study published Monday.

Humans have already wiped out hundreds of species and pushed many more to the brink of extinction through wildlife trade，pollution，habitat loss and the use of toxic substances. The findings published in the scientific journal Proceedings of the National Academy of Sciences（PNAS） show that the rate at which species are dying out has accelerated in recent decades.

Gerardo Ceballos González， a professor of ecology at the National Autonomous University of Mexico and one of the authors of the study， said approximately 173 species went extinct between 2001 and 2014. “173 species is 25 times more extinct species than you would expect under the normal extinction rate.” he told CNN in an email. He and his team found that in the past 100 years， more than 400 vertebrate（脊椎動(dòng)物的） species went extinct. In the normal course of evolution， such extinctions would have taken up to 10，000 years.

Mass extinctions are just as severe as their name suggests. There have been five mass extinction events in the Earths history， each wiping out between 70% and 95% of the species of plants， animals and microorganisms. The most recent， 66 million years ago， saw dinosaurs disappear. The past events were caused by catastrophic changes of the environment， including massive volcanic eruptions or collision with an asteroid.

The sixth mass extinction， the one happening now， is different： Scientists said its caused by humans. Many endangered species are dying in large numbers due to the trade in wild animals and plants.

1. What does the underlined word “toxic” in Para. 2 mean？

A. Poisonous.

B. Useful.

C. Alternative.

D. Environment?friendly.

2. How does the writer convince readers of the seriousness of the mass extinctions？

A. By listing reliable statistics.

B. By mentioning some news from CNN.

C. By imagining a picture of the extinctions.

D. By explaining the history of the extinctions.

3. What is the purpose of the last paragraph？

A. To explain the cause of the coronavirus crisis.

B. To warn humans to get rid of their wrong actions.

C. To show the authors concern about the endangered species.

D. To tell the difference between the fifth and sixth extinction.

Sentence for writing

The most recent， 66 million years ago， saw dinosaurs disappear.

【信息提取】感官動(dòng)詞see，witness，hear等可以用在擬人化的句子中，以增加句子的生動(dòng)性，此時(shí)句子的主語(yǔ)為物。

【句式仿寫】在過(guò)去的10年里，中國(guó)發(fā)生了巨大的變化。