题干
—Why was he unhappy yesterday?
—A letter from home ______ an attack of homesickness.
A：set off
B：set out
C：set about
D：set u
答案(点此获取答案解析）
A
A：set off
B：set out
C：set about
D：set u
是实数，且
是纯虚数，则
( )
