$\frac{a^2-1}{a^2+4a+4}$$÷\frac{a+1}{a+2}$

注意：1）词数100左右；2）可以适当增加细节，以使行文连贯。

Dear Lucy,

Yours truly,

Li Hua

一项工程，甲队独做需要20天完成，乙队独做需要30天完成．现在由甲队施工一天，然后由乙队接替甲队施工一天，第三天再由甲队接替乙队施工一天…，如此交替，最后乙队结束工作，多少天完成任务？

短文改错。

    One summer evening, I was playing and ____ some childs ____ by a river. We saw a lot of frogs(青蛙) in the water. One of us said, “Let's to see ____ who can Catch most ____ frogs.” Then we began. After while____  we caught a lot. We are ____ having a good time when a farmer shouted at us. “Don't caught ____ frogs!” Then he told us how importance ____ they are to farming. They eat a lot of bad insects(害虫) every year, Caught ____ frogs must be stopped. After hear ____ that, we felt very sorry.