As is known to all, the financial crisis firstly broke out in the United States which

_____ the group of developed countries. [ ]

A. belonging to

B. was belonging to

C. belongs to

D. is belonged to

燃油锅炉刚启动时，雾化选择开关置于（）位置。

（A）蒸汽

（B）空气

（C）中间

（D）任意