Sharks play a vital role in the oceans in a way that the average fish does not. Most sharks serve as top predators at the pinnacle of the marine food pyramid, and so play a critical role in ocean ecosystems. Directly or indirectly they regulate the natural balance of these ecosystems. Sharks tend to eat very efficiently, 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 cause harm to the ecosystem by becoming too populated. The ocean ecosystem is made up of very complex food webs. For the most part, “keystone” species, meaning that removing them may cause the whole structure to fall apart, including key fisheries such as tuna and other important fish species that maintain the health of coral reefs.
Therefore, we should protect sharks because doing so is to protect the whole ecosystem.
58. What's the main reason for killing sharks in Asia?
A. Shark fins are in great need.
B. People kill them out of fear.
C. Sharks often attack swimmers.
D. Sharks break the balance of the sea.
59. After the number of cow nose rays greatly increased, ________.
A. water quality improved as well
B. bay scallops grew out of control
C. the health of coral reefs worsened
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