题干
-- Mum, must I do my homework now?
-- No, you ______. You can do it after supper.
A：mustn't
B：can't
C：shouldn't
D：needn't
答案(点此获取答案解析）
D
-- Mum, must I do my homework now?
-- No, you ______. You can do it after supper.
A：mustn't
B：can't
C：shouldn't
D：needn't
恒成立的一个充分不必要条件是（ ）