Final answer:
The bulb on a TXV exerts a variable influence on the valve, adjusting the flow of refrigerant based on temperature changes. The correct answer is c.
Step-by-step explanation:
On a Thermal Expansion Valve (TXV), the bulb exerts a variable influence on the valve. The TXV is a component in refrigeration and air conditioning systems that regulates the flow of refrigerant. The bulb, which is attached to the TXV, is filled with a gas or liquid that expands or contracts in response to temperature changes. This expansion or contraction exerts pressure on a diaphragm within the TXV, causing the valve to open or close accordingly. Therefore, the correct answer is c. Variable.