题目

⑴ 求和：； ⑵ 求和：； ⑶ 求和：. 答案：⑴⑵⑶ 解析:⑴ 原式      . ⑵ 原式      . ⑶             .---- Look! Everything here is under construction. ---- What’s the pretty small house that ____________ for? A．is being built       B．has been built      C．is built            D．is building