The pressure of B and C sealing gas is P=P0-mgS, where m is the total gravity of piston and sand hopper. With the leakage of fine sand, M decreases, the atmospheric pressure P0 remains unchanged, the piston moves upward, and the pressure of the enclosed gas P increases, so B is wrong and C is correct.
D, thermistor resistance decreases, temperature increases. From the fact that the internal energy of an ideal gas with a certain quality is only related to the temperature, it can be known that the internal energy of the gas is increased. So, d is wrong.
So choose C.