与牙周病有关的全身疾病有（）
A.糖尿病
B.肾小球肾炎
C.肝炎
D.肺结核
E.高血压
参考答案：A
The number of people invited __________ fifty, but a number of them __________ absent for different reasons
A．were ; was
B．was ; was
C．was ; were
D．were ; were
描述液体运动有迹线和流线的概念：（）
A.流线上质点不沿迹线运动
B.质点运动的轨迹称为流线
C.流线上质点的流速矢量与流线相切
D.质点的迹线和流线都重合
