常用的选矿方法有几种？
参考答案：
一般常用的选矿方法有三种即；浮选法、磁选法、重选法。
--- What' s the matter with Della?
--- Well, her parents wouldn't allow her to go to the party, but she still __
A．hopes to
B．hopes so
C．hopes not
D．hopes for
形成新物种的主要标志是（）
A.形成地理隔
B.基因频率的改变
C.产生了生殖隔离
D.基因型频率的改变
