While Mary a letter, the children were playing outside.
A. wrote
B. writes
C. is writing
D. was writing
网友回答
A. wrote
B. writes
C. is writing
(答案→)D. was writing
解析：根据语境可知此句的含义是Mary在写信的时候，孩子们正在外面玩。此题重点考查的是while引导的状语从句表示当…的时候。其强调的是两个动作同时进行，并且经常用进行时态，故选D。