He's not seen his mother for a long time, __________ he?
A:does
B:has
C:doesn't
D:hasn't
下列地区缺水最严重的是( )
取甲乙两个瓶子,甲瓶中装有萌发的种子;乙瓶中装有未萌发的种子;两瓶分别用橡皮盖严,放在温暖的地方,一天后把燃烧着的蜡烛分别放入两瓶内,观察到的现象是( )