In case of unsteady fluid flow, conditions & flow pattern change with the passage of time at a position in a flow situation. Which of the following is an example of unsteady flow ?

A. Discharge of water by a centrifugal pump being run at a constant rpm
B. Water flow in the suction and discharge pipe of a reciprocating pump
C. Water discharge from a vertical vessel in which constant level is maintained
D. Low velocity flow of a highly viscous liquid through a hydraulically smooth pipe