微笑是婴儿的一种社会性行为，这是婴儿引起他人积极反应的一种手段，研究发现，婴儿的微笑经历以下阶段：自发的微笑

A. He was Zambias first pres ident.
B. He was Zambia s ambassador to the United States .
C. He will be buried on November II.
D. He was Zambias first white president

A. People can listen to more materials there.
B. People can watch more videos there.
C. People are surrounded by different speakers there.
D. People can hear and see the language in a proper context there