干髓术后发生残髓炎者，应进行什么治疗()

A．除去重填物重新失活后再行干髓术

B．拔除患牙

C．除去充填物、进行根管治疗或牙髓塑化疗法

D．不除去充填物，只使用药物消炎

E．除去充填物开放，服用止痛药物、症状消失后重新充填

Luckily ______ to be no one under the tree when it broke down.

A．it happened

B．there happened

C．there used

D．it had