when will he finish writing the book?i am not sure,but he it last night. 用write填空

问题描述:

when will he finish writing the book?i am not sure,but he it last night. 用write填空
是write还是was writing?

was writing
他将会什么时候写完他的书?我不确定,但是昨天晚上(这个时候)他正在写.