My Old Classmate also mentioned some important events that _______ from 1993 to 2013.

A．had happened

B．was happened

C．happened

D．has happened

以下提供若干组考题，每组考题共用在考题前列出的A、B、C、D、E五个备选答案。请从中选择一个与问题关系最密切的答案。

活髓牙全冠修复应采用的粘固剂是

A．自凝塑料
B．热凝塑料
C．磷酸锌粘固粉
D．玻璃离子粘固剂
E．环氧树脂粘固粉