管道的压降由（）组成The pressure drop in the pipeline consists of three parts：

A、消耗于摩阻的压降Pressure drop consumed by friction；
B、气体上升克服高差的压降The rise of gas overcomes the pressure drop of height difference；
C、流速增大引起的压降The rise of gas overcomes the pressure drop of height difference
D、气体内摩擦造成的压降Pressure drop due to internal friction of a gas