The correct answer is B) To transmit the bulb pressure (proportional to the coil temperature) to the thermal expansion valve diaphragm. The purpose of the sensing line connected to the thermal bulb at the evaporator coil outlet is to transmit the pressure inside the bulb, which is proportional to the temperature of the coil, to the diaphragm of the thermal expansion valve. This allows the thermal expansion valve to modulate the flow of refrigerant to the evaporator coil based on the temperature of the coil, ensuring efficient operation of the refrigeration system. 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 valve. Option C is incorrect as the sensing line does not directly open or close the solenoid valve. Option D is incorrect as the sensing line does not control the back pressure regulating valve.