对于颌骨缺损修复原则的描述，错误的是（）

A.永久性修复越早越好

B.尽可能恢复生理功能

C.尽量保护预留组织

D.良好的固位是颌骨缺损修复成功的关键

E.修复体总重量不超过20g

30.   It was once called the Sea of Bamboo, but now only one fifth of the area ______ covered with bamboo, and sixty percent of other plants ______ taken the place of the bamboo.

A．are; have

B．is; has

C．is; have

D．are; has