—Why was he unhappy yesterday?
—A letter from home an attack of homesickness.
A. set off
B. set out
C. set about
D. set up
网友回答
(答案→)A. set off
B. set out
C. set about
D. set up
解析：考查短语辨析。set off爆发，set out出发，set about着手做，set up 建立，句意：昨天他为什么不高兴？一封来自家乡的信使他突发了思乡病。所以选A。