The correct answer is B) Permits the return of cargo to the suction side of the pump. The purpose of the relief valve on a cargo pump is to provide a means of recirculating cargo back to the suction side of the pump. This prevents excessive pressure buildup in the discharge line, which could damage the pump or associated piping. The relief valve allows cargo to be redirected back to the pump inlet when the discharge pressure exceeds a predetermined set point, rather than shutting down the pump entirely. The other answer choices are incorrect because they do not accurately describe the primary function of a cargo pump relief valve. Option A is incorrect as the relief valve does not allow for simultaneous tank filling. Option C is incorrect as the relief valve does not provide emergency shutdown capability. Option D is incorrect as the relief valve does not remove vapors, but rather recirculates liquid cargo.