The sports meet, originally due to be held last Friday, was finally _____ because of the bad weather.

A．set up

B．broken down

C．worn out

D．called off

患者，女，40岁，A5678B45678缺失，余留天然牙稳固，牙槽骨丰满，A4B3做基牙，铸造支架修复。

可摘局部义齿卡环设计时，应该避免使用过多的卡环，卡环数量以多少为宜

A．超过5个

B．不超过4个

C．不超过3个

D．不能超过6个

E．不能超过7个

F．不能超过8个