牙脱位后，可能发生的并发症是（）
A.牙髓坏死
B.牙髓腔变窄或消失
C.牙根外吸收
D.边缘性牙槽突吸收
E.以上均正确
参考答案：E
________by the rising price of gas, many car owners use their cars less frequently. [ ]
A. Driven
B. Being driven
C. To drive
D. Having driven
心室舒张时，防止血液逆流的是（）
A.主动脉瓣和肺动脉瓣
B.二尖瓣和三尖瓣
C.主动脉瓣和二尖瓣
D.肺动脉瓣和三尖瓣
E.主动脉瓣和三尖瓣
