Which of the following represents a heat pump?

• A. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/414-133-1.png">
• B. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/414-133-2.png">
• C. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/414-133-3.png">
• D. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/414-133-4.png">