The airport was built during the war,but for some reason it could not be used then.
问题描述：
The airport was built during the war,but for some reason it could not be used then.
后面是不是then,为加它,不加行不行?
答
句意为.机场在战时修建,但由于某种原因那时并未启用.then 此处为 那时 加它表示时间,与could呼应.但不影响句意.可有可无吧.