选c
首先,根据语态要用现在进行时
另外,work on 是固定短语,放在原句中,解释为在解数学题,意思相符.
------What are you doing?
------What are you doing?
------I'm ____ the math problems.
A.work B.working C.working on D.working of
------I'm ____ the math problems.
A.work B.working C.working on D.working of
英语人气：388 ℃时间：2020-05-07 01:26:27
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