在粗盐提纯的实验中,蒸发时正确的操作是( )
A:把浑浊的液体倒入蒸发皿内加热
B:开始析出晶体后用玻璃棒搅拌
C:待水分完全蒸干后停止加热
D:蒸发皿中出现大量固体时即停止加热
— Andy, it's late. Why not go to bed.
— Helen hasn't come back yet. I____ (wait )for her.