牙外伤的并发症有________、牙髓休克、________、________和________。
参考答案:牙髓损伤 牙髓坏死 牙髓钙化 牙根吸收
____ so many women received college education as today.
A.Never are there
B.Never have
C.Never had
D.Never did
人体对机械振动的反应取决于()。
A.振动的频率
B.振动作用的方向
C.人的心理状态
D.暴露时间
E.振动的强度