下列不属于生命现象的是 [ ]
A．牛吃草
B．水结成冰
C．雁南飞
D．蝌蚪长成青蛙
答案：B
Alice, are you ready? We'll go out for a picnic _____ nine o'clock.[ ]
A. in
B. after
C. until
简述悬浮剂优点与缺点。
