AB. Insert the ceramic plate. According to the decisive formula C=?s4πkd, it is known that the capacitance increases and the potential difference remains unchanged. Then Q=CU is known, and the charge of the capacitor increases. There is a brief current flowing in the counterclockwise direction in the circuit. Therefore, A and B are wrong.
If CD and potential difference remain unchanged, and d decreases, the electric field intensity will increase, and the electric field force on the charged droplets will increase, which is greater than gravity, and will accelerate upward. Therefore, C is wrong and D is correct.
So choose: D.