The correct answer is D) To transmit the bulb pressure (proportional to the coil temperature) to the thermal expansion valve diaphragm. The sensing line connected to the thermal bulb at the evaporator coil outlet is used to transmit the bulb pressure, which is proportional to the coil temperature, to the thermal expansion valve diaphragm. This allows the thermal expansion valve to open and close based on the temperature of the refrigerant leaving the evaporator, ensuring the proper amount of refrigerant is supplied to the evaporator coil. The other answer choices are incorrect because they do not accurately describe the purpose of the sensing line. Option A is incorrect as the sensing line does not directly control the solenoid bellows. Option B is incorrect as the sensing line does not directly open or close the solenoid valve. Option C is incorrect as the sensing line does not control the back-pressure regulating valve.