When you are on the bus to work in the morning, smile to the people sitting beside you, yo

When you are on the bus to work in the morning, smile to the people sitting beside you, you will get his smile .
A. in place
B. in need
C. in return
D. in relief

A. in placeB. in need(答案→)C. in returnD. in relief解析：in place适当的； in need需要； in return 作为回报；in relief减轻，句意是早上坐车上班时，如果你对你对邻座微笑，作为回报你将得到他的一个微笑。故选A。

就是这个解释