影响流体阻力的因素有（）。
A、流体的粘度
B、管闭的粗糙程度
C、管线的管径
D、管线的长度
参考答案：A, B, C, D
Although he was disabled when he was only ten years of age,yet he aimed _____,for which his classmates spoke ______of him.
A．high;high
B．highly; highly
C．highly; high
D．high; highly
在专用排瓦斯巷进行巷道维修时，瓦斯浓度必须低于（）
A.2.0%
B.1.5%
C.1.0%
