The general relationship between speed N, head H, power P and discharge Q for a centrifugal pump is_________________?
A. Q∝N : H∝N2 : P∝N3
B. Q∝N2 : H∝N3 : P∝N
C. Q∝N : H∝N3 : P∝N2
D. Q∝N3 : H∝N : P∝N2