_______ to the cold for a long time will do harm to your face.

A．Exposed

B．Being exposed

C．Exposing

D．Having exposed

下面哪项是牙髓疾病的物理因素（）

A.细菌感染

B.消毒药物刺激牙髓

C.充填材料渗漏

D.慢性咬合创伤

E.牙周炎症