The role of the "flow restriction"（Line 6, Para. 2) in a heat pump is to____A．measure accu

The role of the "flow restriction"(Line 6, Para. 2) in a heat pump is to____

A．measure accurately the flow rate of the refrigerant mass at that point

B．reduce the pressure to bring about the evaporation and cooling of refrigerant

C．stop the refrigerant from further moving

D．reverse the direction of refrigerant flow when needed