—Why do you look so puzzled?—Oh，I ________ over a most difficult maths problem.A_刷题宝

题干

—Why do you look so puzzled?
—Oh，I ________ over a most difficult maths problem.

A．thought	B．have thought
C．am thinking	D．think

上一题下一题 0.85难度单项选择更新时间:2014-03-11 07:11:48

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