A, the zero scale of the ohmmeter is at the right end, and the pointer of the ohmmeter gradually deflects to the right, so the resistance of the thermistor becomes smaller. So, A is wrong.

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.