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

女，26岁。右上后牙龈肿痛1周，口服消炎药治疗无效。检查：牙体颊侧牙周脓肿形成，叩痛（+），冷测反应同对照牙，牙周袋8mm，应急处理应是（）

A.局部麻醉下开髓

B.龈上洁治

C.龈下刮治

D.脓肿切开引流

E.全身药物治疗