问题描述：
though without hans ,mafuxing ___chinese language in a rural primary school in huangzhong,qinghai for 30years.
A would teach B will have taught C had been teaching D has been teaching
the answer is D ,tell me why ,and why not use the others?
A would teach B will have taught C had been teaching D has been teaching
the answer is D ,tell me why ,and why not use the others?
问题解答：
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