问题
单项选择题
The human beings have polluted the environment seriously. It is time the United Nations must take some measures.
A. take
B. taking
C. to take
D. took
答案
参考答案：D
解析： 结构应用
本句考察的是虚拟语气结构。It is(about/high)time that...句型用虚拟语气，其谓语部分用一般过去时，因此D为答案。