任务型阅读。

It is spring. We are born (出生) in a river. We are small and black. We look like "balls". Then we are still black. We have big heads. We have long and thin tails. We swim in the river. Now we have four legs. Our mouths are big. Our tails are getting shorter and shorter. Now it's summer. We're green. We have big eyes, but we have no tails. We're good for the crops (庄稼). Who are we? Do you know? Yes, we're frogs (青蛙).