小蜗牛和妈妈散步,看到很多动物走得都很快,而它们却—步—挪,小蜗牛伤心地问妈妈:“为什么从我出生,我的背上就顶着—个又厚又重的壳呢?”妈妈说:“因为我们没有骨骼,又爬得慢,所以要一个坚硬的壳来保护自己。”小蜗牛委屈地说:“毛毛虫姐姐没有骨头,也爬得慢,她为什么不用顶着一 A small snail walks with her mother and sees many animals walking very fast, and yet they - step - move, the little snail sadly asks her mother: “Why is it that I was born, my back was held - a thick and heavy Shell? ”Mom said:“ Because we do not have bones, and climb slowly, so a hard shell to protect themselves. ”Small snail said aggrievedly:" Caterpillar sister no bones, but also crawling slowly, why is she Do not have to withstand one