The correct answer is C) The valve should indicate fully open at 3 psig and should indicate fully closed at 15 psig. This is correct because in a properly adjusted pneumatically operated diaphragm actuated control valve, the valve should be fully open when the pilot pressure is at the lower end of the operating range (3 psig) and fully closed when the pilot pressure is at the upper end of the operating range (15 psig). This ensures the valve responds appropriately to the control air pressure supplied to the pilot controller, which is designed to operate the valve within this 3-15 psig pressure range. The other options are incorrect because they do not correctly describe the expected valve position indications at the specified pilot pressures for a properly adjusted control valve system.