—What's your favorite subject?
—________ favorite subject is P.E. [ ]
A. His
B. Her
C. My
C
简述气质的激素理论。
有两个大小恒定的力,作用在一点上,当两力同向时,合力为A,反向时合力为B,当两力互相垂直时,其合力大小为()
A.
B.
C.
D.