Question

7. They        ，but both of them went to bed early last night and totally forgot about it. (set)

他们应该着手做准备，但他们昨晚却早早地上了床，完全忘了这件事。

Answer 1

7. should have set about making / set out to make preparations考查set out to do sth. / set about doing sth.和虚拟语气的用法。set out to do sth. / set about doing sth.都是"着手做某事"的意思。从句意判断是他们本该着手做而没做，因此用should have done;, shouldn' t have done表示本来不应该做某事而实际做了。含有指责对方或自责的含义。