the fire lasted for 20 days,(during that time)the whole forest was destroyed.
问题描述：
the fire lasted for 20 days,(during that time)the whole forest was destroyed.
为什么不能填during which time
答
如果用which,那应该是during which,即the fire lasted for 20 days,during which the whole forest was destroyed.这句是非谓语从句,which 就整个指代了for 20 days.如用during which time,那么这个which即与time重复,或许你可以这么理解.