题干
—Do you know ________?
—All of them ________ the museum.
A：where are the students; have gone to
B：where are the students; have been to
C：where the students are; have gone to
D：where the students are; have been to
答案(点此获取答案解析）
C
，则关于
的方程
有7个不同实数解的充要条件是( )