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
_____ defeated, they didn’t lose heart
we first heard of the man referred to as a computer specialist in software.
How we wish he ______ present! [ ]
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Mrs. Black doesn’t believe that her son is able to design a digital camera, ______?[ ]