一般认为历史上最早的社会心理学研究,是围绕()的哲学争辩。
A.遗传和环境
B.社会分层
C.本能和教育
D.人性
参考答案:D
The little boy________in the mud all morning.No wonder he is dirty from head to foot. [ ]
A. has played
B. is playing
C. has been playing
D. was playing