题目内容
Mr. Wu _____ this math problem _____him many times, but he still doesn’t understand it.
A. explains; to B. have explained; for
C. has explained; to D. explained; with
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题目内容
Mr. Wu _____ this math problem _____him many times, but he still doesn’t understand it.
A. explains; to B. have explained; for
C. has explained; to D. explained; with