Select the correct sentence or sentences in the passage. Which two sentences in the passage are simple sentences? Thermal Mass (1) Thermal mass describes the ability of material, such as brick, stone, or cement walls, to store heat. (2) The temperature might be high during the day, but if a building does not have enough thermal mass, the temperature inside will drop along with the outside temperature. (3) One way to help even out the temperature inside a building is to include a lot of thermal mass when the structure is built. (4) During the day, heat from the warm air or sunlight outside is absorbed by the walls. (5) At night, some of this heat is released inside the building as the outside temperature drops. (6) This process is called passive solar heating because it does not involve mechanical heating devices.