A:①②
B:①④
C:①③
D:②④
—Oh, we won't have supper_______ your dad comes back.
be aware of, (be)scared to death, upside down, at close range, wake up, be fond of, get close to, in danger of
已知下列命题中:(1)若k∈R,且kb→=0→,则k=0或b→=0→,(2)若a→·b→=0,则a→=0→或b→=0→(3)若不平行的两个非零向量a→,b→,满足|a→|=|b→|,则(a→+b→)·(a→-b→)=0(4)若a→与b→平行,则a→·b→=|a→|·|b→|其中真命题的个数是( )
分布在第三级阶梯上的主要地形类型是 ( )