The correct answer is D) Lower than normal suction pressure. A small obstruction at the thermostatic expansion valve inlet will restrict the flow of refrigerant entering the valve, resulting in a lower than normal suction pressure in the refrigeration system. This is because the expansion valve controls the amount of refrigerant flowing into the evaporator, and any obstruction at the inlet will reduce the flow, leading to a drop in suction pressure. The other options are incorrect: A) Higher than normal discharge pressure is not correct, as the obstruction is at the inlet, which would affect the suction side, not the discharge side. B) Expansion valves are not designed to pass small foreign particles, and an obstruction can cause issues. C) Ice formation is not the sole cause, and the obstruction will not necessarily melt due to superheat.