If you want to ________ a pleasant visit, find out as much as possible about the manners and customs of your host country.

A．ensure

B．deserve

C．secure

D．serve

患者，男性，27岁，经翻瓣、去骨，劈开拔除右下近中阻生第三磨牙，4天后出现持续性剧痛，向耳颞部放射，检查见拔牙创空虚，牙槽骨壁表面有灰白色假膜覆盖。最可能的诊断是（）。

A.下颌骨骨折

B.拔牙后正常反应

C.干槽症

D.邻牙在拔牙时受到损伤

E.邻牙急性根尖周炎