题干
Mike has no time to buy a gift for Alice. So he doesn’t know _______ her birthday party.
A：whether to take part in
B：if to take part in
C：whether to join
D：if to join
答案(点此获取答案解析）
A
的方程
，给出下列四个命题：
，使得方程恰有2个不同实根；