had been boiling
was taken
因为有"before"
所以前一个空表示在水被从炉子上拿走之前,这三分钟水一直在被煮,是过去完成时的进行语态。
而且过去完成时表示的事过去的动作的再前面一个动作。既然后一个空用了"was taken",那就要因该用过去完成时。
had been boiling was taken
这壶水在炉子上煮了三分钟才拿下来
the kettle water boiled for 3 minutes before it had taken away from the stove.
had boiled, was taken.