问题描述：
the robots have been sent to repair the damaged nuclear power station in Japan
It was the first time that the robots __have been sent____________ to repair the damaged nuclear power station in Japan.横线处为什么用现在完成时?
横线处改为 had been sent
不好意思打错了
It was the first time that the robots __have been sent____________ to repair the damaged nuclear power station in Japan.横线处为什么用现在完成时?
横线处改为 had been sent
不好意思打错了
问题解答：
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