问题描述：
after 前后时态与after 的位置有关吗
The furnace was turned off six minutes after the last pellet had been charged.
Six minutes after the last pellet was (had been) charged,the furnace was turned off.
为什么后面的句子after后可以用过去式
The furnace was turned off six minutes after the last pellet had been charged.
Six minutes after the last pellet was (had been) charged,the furnace was turned off.
为什么后面的句子after后可以用过去式
问题解答：
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