问题
选择题
I have __________ the problem for two hours, but I haven't __________.[ ]
A. worked on, worked out it
B. worked at, worked it out
C. worked on, worked it out
答案
答案：C
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I have __________ the problem for two hours, but I haven't __________.[ ]
A. worked on, worked out it
B. worked at, worked it out
C. worked on, worked it out
答案：C