When a series of wheel loads crosses a simply supported girder, the maximum bending moment under any given wheel load occurs when

• A. the centre of gravity of the load system is midway between the centre of span and wheel load under consideration
• B. the centre of span is midway between the centre of gravity of the load system and the wheel load under consideration
• C. the wheel load under consideration is midway between the centre of span and the centre of gravity of the load system
• D. none of the above