常用选矿方法有磁选、浮选和（）法。
参考答案：重选
—I have a headache. I can't sleep.
—_______[ ]
A. You are bad.
B. I'm sorry to hear that.
C. Why do you say that?
D. Thank you
搜救协调人是（）的搜救管理人员。
A.最高层次
B.中间层次
C.较低层次
D.最低层次
