A:①②
B:②④
C:①②④
D:①③④
蜜蜂是典型的社会行为的动物,在花丛中采蜜的蜜蜂所处的发育时期是( )
The winner of the singing competition was a girl named Zhang Mei from China.
若平面α与β的法向量分别是a→=(1,0,﹣2),b→=(﹣1,0,2),则平面α与β的位置关系是( )