I _____ the prolem until he explaind it.A.understood B.did not un_英语解答

I _____ the prolem until he explaind it.A.understood B.did not understand C.had not understood D.
had understood

人气：379 ℃　时间：2020-03-26 18:10:13

解答

选B
not ……until 直到……才……
句意是：直到他解释了我才明白这个问题.