I found he_______(explain) the problem to his students when I wal_其他解答

I found he_______(explain) the problem to his students when I walked into his office.

人气：481 ℃　时间：2019-11-21 01:10:57

解答

was explaining过去进行时,表示我走进办公室的时候他正在进行,是同时发生,且为过去,所以用过去进行时