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问题 选择题

哪种动物最高等？（　　）

A．青蛙

B．鲸

C．麻雀

D．鲫鱼

答案

解；生物进化的历程是结构由简单到复杂，由水生到陆生，由低等到高等．而脊椎动物的进化历程是鱼类（鲫鱼）→两栖类（青蛙）→爬行类→鸟类（麻雀）和哺乳类（鲸），鸟类和哺乳类相比，哺乳类是胎生哺乳比鸟类的卵生，更加适应多变的生活环境．综上所述A、C、D选项不符合题意，只有B选项符合题意．

故选：B

单项选择题

14，6，2，0，( )

A．-2

B．1

C．-1

D．0
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单项选择题

"A rolling stone gathers no moss(苔藓) ," but there is one living animal that does gather moss, the three-toed sloth (树獭) of South America. This slowest-moving member of the animal kingdom is so inactive that moss actually gathers on its body and turns it green——strange as it seems!
Most of the sloth’s life is spent motionless, hanging upside down from a limb. And that is the way its hair grows. Long and coarse, the strands (串) from receptacles (花托) for the damp jungle algae (水藻) that turn the brown fur a mossy green. Actually this moss helps the animal survive because it serves as a perfect camouflage against the leaf trees and hides the sloth from the jungle’s swift - moving hunters. The sloth would have little chance of survival on the ground. With long, curved claws hooked over the limb of a leafy tree, it spends the long hot hours during the day drowsing and eating. Inch by inch, it strips the leafy limbs bare and crawls slowly down the trunk to find a new dining spot, but only at night.
In addition to looking rather like a vegetable, the sloth is a strict vegetarian. Running out of its favorite leaf is about the only thing that will make a sloth move. Then its appetite may even force the animal into swimming a stream to reach a juicy succulent(多汁的植物). It will also force it into fighting to keep the tree all to itself. The sloth is lazy and prefers to be alone, but it will tolerate its own relatives!

According to the passage, the sloth will move about when ______.

A．it senses a coming danger

B．it is forced to swim on a hot day

C．it is short of its favorite food

D．it wants to keep itself to itself
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