题目内容：

    China says 16 endangered finless porpoises（江豚）have been found dead since the beginning of the year and experts blame water pollution and climate change for pushing the species toward extinction．

The freshwater porpoise-popularly known in Chinese as the"river pig"-mainly lives in China's Yangtze River and two lakes linked to the river．

Authorities（官方）have discovered 10dead porpoises in Dongting Llake in the central province of Hunan since March, according to a statement by the government of Yueyang City, which is located on the lake's shore． Another six dead porpoises have been found in Poyang Lake in the eastern province of Jiangxi since the beginning of the year． Experts warn that the species will be extinct within a matter of years．

Wang Kexiong, a researcher at China's Institute of Hydrobiology, said water pollution, shipping and sand dredging（挖掘）were all possible contributing factors to the recent deaths．

Many rivers in China have become heavily polluted with poisonous waste from factories and farms-pollution blamed on more than three decades of rapid economic growth and slow enforcement（实施）of environmental protection laws．

The report said climate change also could be to blame as the dry weather has caused water levels to drop and makes it more difficult for the porpoises to find food． Tests have shown that some of the porpoises are believed to have died of starvation（饥饿）．

In 2006, China was estimated（估计）to have only 1,200 finless porpoises left． That same year, the Baiji-a freshwater dolphin also native to the Yangtze River-was declared extinct． Earlier this year, a survey found just 65"river pigs"in Dongting Lake and 300-400 in Poyang Lake．

Following the recent deaths, Yueyang City promised to investigate and increase protection of the remaining porpoises in Donting Lake．

1.How many river pigs are estimated to live in Dongting Lake？

A.49

B.55

C.59

D.65

2.The following factors of river pigs' deaths are mentioned EXCEPT__________．

A.water pollution

B.climate change

C.food shortage

D.illegal fishing

3.We can learn from the text that__________．

A.river pigs' deaths can be reduced if measures are taken in advance

B.river pigs' deaths are completely caused by human beings' activities

C.climate change is likely to stop economic growth in China

D.economic growth always has a negative effect on the environment

4.The number of river pigs is listed in Paragraph 7 to________．

A.show they have become extinct

B.call for more effective protection

C.show they are on the edge of extinction

D.show the importance of raising them in labs