After living with his grandparents in the countryside fort en years, the boy returned to

The big city____his parents worked.

A．which

B．where

C．that

D．when

如图是某运动员进行射箭比赛的情形，下面说法正确的是：

A.被拉弯的弓具有弹性势能

B.手拉弓弯，说明力能改变物体的运动状态

C.手对弓的拉力大于弓对手的拉力

D.运动员松手时弓的弹性势能将转化为箭的动能