影响流体沿程阻力损失的因素是（）。
A.运动状态
B.管道内粗糙度
C.管道结构尺寸
D.流体黏度
参考答案：A, B, C, D
Green products are becoming more and more popular because they are environmentally_______.
A．friendly
B．various
C．common
D．changeable
正常关节腔内液体为 （）
A.2～4ml
B.3～5ml
C.0.1～2ml
D.＜10ml
E.＜5ml
