任务型阅读：回答下列问题，第五题为翻译划线句子。
One day, a baby snail（蜗牛） found that he had to carry a big and heavy shell（壳） at any time. He was confused(困惑的), so he went up to his mother and asked, “ Why was I born with a shell that grew so hard and heavy?” His mother said, “Because we don't have bones（骨头） to hold us up. We can only move slowly, so we need a shell to protect us.”
The baby snail asked again, “The caterpillar(毛毛虫) has no bones, either, and she can't move quickly. Why can she live without a shell?” The mother snail answered, “That's because a caterpillar will become a butterfly. She can fly high into the sky. The sky can protect her.”
The baby snail had one more question, “But the earthworm(蚯蚓) moves like us. He has no bones and he won't turn into a butterfly. Why doesn't he carry a hard and heavy shell?” His mother said, “He can dig a hole and hide in the ground, and then the earth can protect him.”
The baby snail then cried, “We are so poor! We have no protection from the sky or from the ground!” His mother smiled at him, “That's why we have a shell. My dear, imagine that if we don't have the shells, what will happen to us? Hot sun will dry out our bodies and we'll have nowhere to sleep. What's worse, we'll die in the heavy rain. How terrible it is! We don't depend on the sky or the ground for protection. We should depend on ourselves.”
