when引导的时间状语可以是现在时,主句用一般将来时(情态动词,祈使句),如:
When he comes, I will tell you.
when引导的时间状语用过去时,主句用过去进行时,如:
I was having breakfast when he arrived.
when引导的时间状语用过去时,主句用过去完成时,如:
When we got to the station, the train had already left.
when引导的时间状语用过去进行时,主句用过去时,如:
He arrived when I was taking breakfast.