参考答案:
1.It took him four years to stage this elaborate joke simply to prove that critics do not always know what they are talking about.
2.It took the police nearly an hour to get the traffic on the move again.
3.It struck me that we ought to take action at once.
4.It is natural that they should have different views.
5.It is possible that there is a definite relation between these paintings and the markings that sometimes accompany them.