(单选题)
One of the unanswered questions of September 11th is whether there was anything U.S.
intelligence ______ to stop the attacks.
A.must do
B.could do
C.must have dune
D.could have done
参考答案:D
参考解析:
考查情态动词的虚拟用法。句意:9.11事件中尚未解决的问题就是美国情报机关是否本可以做一些防范措施来阻止这场袭击。must do表示“必须做某事”;could do表示“能够做某事”;must have done是对过去事实的肯定推测,表示“过去一定……”;could have done是对过去事情的假设,表示“本来能做而没有做。”根据句意,故选D。
知识点: