题目

下列说法正确的是（ ） A．煤气泄漏立即打开抽油烟机排气 B．用焚烧法可以处理塑料垃圾 C．用过滤的方法能使硬水软化 D．羊毛和合成纤维都属于高分子化合物 答案：D —There ________ lots of plants here. But now I can’t see any. 　　—That’s the problem. To solve it, we ________ plant trees here. 　　A. used to be; are going to B. are used to be; will 　　C. used to are; are going to D. are used to; will