问题

Why do you look so puzzled?—Oh,I ________ over a most difficult maths problem
A:thought
B:have thought
C:am thinking
D:think
B:have thought
C:am thinking
D:think
正确答案是:
同类题型
Alice looks blue today.—Yes,I asked her,but she wouldn’t say ______ troubled her.
I’ll never forget the days _____ we spent on the small island
You cough heavily all day. I think you really _____give up smoking.[ ]
I think you’ve got to the point_____a change is needed , otherwise you’ll fail .
They promise that the work would all be finished _____ next week