题目内容：

    There is a huge need for shark fins (鳍) in Asian countries. As a result, many sharks are caught and killed. According to reports, sharks are being killed at an shocking rate (速度) of up to 273 million worldwide every year.

Some experts predict that if the killing continues at the current rate, many shark species will be lost forever. It can be very dangerous. Sharks are very important and they should be protected.

In a study of the east coast of the United States, 11 species of sharks were eliminated from their range. Of the 14 species of ocean life that those sharks used to eat, the populations of 12 exploded and caused great damage to the ecosystem. For example, the cownose ray (鳐) population was no longer kept under control by sharks and so grew out of control. As a result, the rays destroyed the population of bay scallops (扇贝), their favorite food. The scallop fishery, which had been in good condition for over 100 years, was destroyed completely. Also, the removal of the scallops most likely had an effect on water quality as they were no longer there to perform their function (功能) of cleaning the water.

Sharks tend to eat very efficiently (高效地), going after the old, sick, or slower fish in a population, keeping that population healthy. Sharks help keep many populations of ocean life to the right size so that those prey (猎物) species don’ t do harm to the ecosystem by becoming too populated. The ocean ecosystem is made up of very complex (复杂地) food webs. For the most part, sharks are at the top of these webs and are considered by scientists to be “keystone” species, meaning that removing them may cause the whole structure to fall apart. Therefore, we should protect sharks because doing so is to protect the whole ecosystem.

1.According to the passage, in Asian, people kill sharks mainly because ________.

A.sharks are dangerous for people B.there are too many sharks

C.shark fins are in great need D.sharks often attack swimmers

2.Which of the following can replace the underlined word “eliminated” in Paragraph 4?

A.Fed. B.Removed. C.Charged. D.Protected.

3.After the number of cownose rays greatly increased, ________.

A.water quality improved as well B.bay scallops grew out of control

C.there are more food for shark D.the local scallop fishery was harmed

4.What can we know about sharks from Paragraph 4?

A.They can’t find enough food to feed on.

B.They never eat the old, sick or slower fish.

C.Their large populations can harm the ecosystem.

D.They play a key role in keeping the ecosystem healthy.