What must a switchman ensure when placing a portable hand trolley to a car?

The correct answer emphasizes the importance of safety and stability when placing a portable hand trolley to a car. Proper footing must be maintained to ensure that the switchman is secure while performing the task. This is essential because maintaining balance and stability helps prevent accidents that could occur due to slips or falls while handling equipment.

The need for proper footing also reflects broader safety protocols in the workplace, where ensuring one's physical stability can mitigate the risk of injury during operations involving heavy or cumbersome tools like a hand trolley.

Other options suggest alternative actions or conditions that are not advisable or safe. For example, placing both ends on the live third rail simultaneously poses significant risks associated with electrical safety. The suggestion that a single switchman can complete the task alone does not consider the best practices for teamwork and safety during handling potentially heavy equipment. Lastly, placing the trolley in reverse order lacks context about the operational procedures and does not specifically relate to the safe handling of the trolley. Maintaining proper footing remains the most universally applicable and critical aspect of the task.