D

If you are afraid of the dark, it’s not a big deal. It’s perfectly normal to feel afraid. After all, animals do, too. “Fear matters,” says Karen Warkentin, an ecologist. “It's a good thing,” she adds, “because fear makes you do things that keep you alive.”

Like kids，many animals experience fear and they respond to the feeling in variety of ways. A frightened turtle pulls its head and legs inside its shell. A small fish will swim away when a big, hungry fish approaches.

Some animals respond to fear in ways you might not expect. The first example is that the fear of being eaten can scare some frogs right out of their eggs. Warkentin made the surprising discovery while studying red-eyed tree frogs in Costa Rica.

In this species, female frogs attach jellylike clumps (果冻一样的块状物) of their eggs to the undersides of leaves. The leaves hang on branches that dangle (悬挂) over ponds. After they hatch from the eggs, the tadpoles (蝌蚪) then fall into the water, where they eventually grow into adult frogs.

Tree frog eggs usually grow for 6 days before hatching. If they sense that a hungry snake is about to attack, however, they can hatch up to 2 days ahead of the schedule. As the snakes are unable to swim, by falling into the water early, the tadpoles can escape.

If hatching early helps protect red-eyed tree frogs from snakes, you might wonder why their eggs don't always hatch sooner. It turns out that hatching early brings its own danger. Once tadpoles land in the water, hungry fish and other animals like to eat them, too. Staying in their eggs for full 6 days, then, allows frog embryos (胚胎) to grow big and strong. This extra growth improves their chances of surviving in the water.

51. It can be inferred from the passage that fears________．

A．help animals grow bigger and stronger

B．are less common among young animals

C．help animals move a lot to fit the environment

D．are more or less important in order for animals to survive

52. We are told in the passage that tree frogs________．

A．face danger both inside their eggs and in the water

B．will grow fast if they fall into the water later

C．are surprisingly clever when inside their eggs

D．stay in their eggs longer if they are frightened

53. Why do the tadpoles hatch up to 2 days ahead of the schedule？Because________．

A．they like falling into the water early

B．they want to grow into adult frogs

C．they sense a hungry snake is about to attack

D．frog embryos can grow strong

54. What is the best title of the passage?

A．What is fear?

B．Why do we feel afraid?

C．You feel afraid, and animals do, too.

D．Fear is a good thing.

55. What do you think would be discussed in the following paragraph?

A．Further explanations as to why tree frogs hatch ahead of the schedule.

B．How the unborn frogs know when a snake is about to attack them.

C．Another example of animals that respond to fear in an unexpected way.

D．How tree frogs improve their chances of survival before falling into the water.
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