问题补充：
While cleaning the room yesterday, I an old photo of my mother.
A. came out
B. came across
C. came about
D. came up with
答案：
A. came out
(答案→)B. came across
C. came about
D. came up with
解析：考查固定词组，came out意思“出现”，came across意思“遇然发现”，came about意思“发生”，came up with意思“想出”，句子意思“昨天当我打扫卫生时，我偶然发现我妈妈以前的照片”，注意when和while的区别：when后跟既可以是短暂性动词又可以是延续性动词；while后只跟延续性动词，所以选B
