矫治前必须有记录患者牙情况的模型，称之为（）
A.记存模型
B.石膏模型
C.上颌模型
D.初模型
E.终模型
参考答案：A
把下列各句改为被动语态。
1. We clean our classroom every day.
Our classroom _____ by us every day.
2. They produce silk in Suzhou.
Silk _____ in Suzhou.
3. They speak English in class.
English _____ in class.
4. He teaches us ten words every class.
Ten words _____ to us _____ every class.
5. We use keys for opening the door.
Keys _____ opening the door.
（）是安装于轻油罐上，防止罐外明火向罐内传播的防火安全装置，与机械呼吸阀和液压安全阀配套选用，串联安装在它们的下面。
A、消防栓
B、呼吸阀挡板
C、阻火器
D、泡沫产生器
