A:四边形
B:五边形
C:六边形
D:七边形
美国是遭受飓风和龙卷风侵袭严重的国家(飓风是一种发源于热带洋面的大气涡旋,在太平洋地区称台风) 龙卷风频发与该区域地形有直接关系,美国的地形地势特征是 ( )
A: Who's that ____( boy / girl) ?
B: He's my brother.
A: Is the ____( man / woman) your mother?
B: Yes, she is.
A:____ (What's / Who's) that man?
B: Guess.
A: Is ____( he / she) your father?
B: No, he isn't.____ (She's / He's ) my teacher.
能证明乙酸是弱酸的实验事实是( )