题干
Studying in groups is necessary __________ you want to do well in school.
A：if
B：until
C：unless
D：though
答案(点此获取答案解析）
A
Studying in groups is necessary __________ you want to do well in school.
A：if
B：until
C：unless
D：though
［(1-x)(x+3)］的递减区间是（ ）