问题详情

A dolphin(海豚) looks more like a fish than certain fishes do. It is an excellent swimmer. The dolphin seems to flash through the water. Like fish, dolphins are completely at home in the water. There they play, feed, sleep, and give birth to their young. Dolphins live in the sea and can live only in the sea.
Yet they are not fish. A dolphin must come to the surface to breathe. Fish can take oxygen from the water.
Dolphins cannot. Like us, they breathe with lungs and must take their oxygen from the air. And they are mammals (哺乳动物).
Most mammals are land animals. Dolphins are evolved (进化) from land animals. Long ago, dolphin ancestors (祖先) left the land for the sea. Among the animals was a kind that would become the dolphin we know. No one is sure exactly what kind of animal it was. But there is reason to think it was related to grass-eating animals like the cow. Modern dolphins are fish-eaters. Yet their stomachs are like those of animals that eat plants. The make-up of their blood is also like that of grass-eating animals.
The best title for this passage is______.
A．Dolphins
B．Fish
C．Mammals
D．Cows请帮忙给出正确答案和分析，谢谢！