—Why does Jane look unhappy today?.
— A letter from her brother a wave of homesickness.
A. set out
B. set off
C. set about
D. set up
网友回答
A. set out
(答案→)B. set off
C. set about
D. set up
解析：考察动词短语辨析。A出发，动身；B引起，使…发生；引爆；C出发；D建立，设立；句意：—为什么Jane今天看上去不开心？—来自哥哥的一封信让她想家了。根据句意说明本句的set off指“引起”.故B正确。