What must be done before proceeding over a dual control switch that is operated by hand?

Before proceeding over a dual control switch that is operated by hand, it is essential for the train to stop. This procedure is crucial to ensure the safety of the crew and the integrity of the switch operation. Stopping the train allows for a thorough check of the switch position and provides the opportunity to properly align the switch manually if needed.

By halting the train, the crew can confirm that it is safe to proceed and that the switch is set in the correct direction for the train's movement. This helps prevent accidents that could result from misaligned switches and adds a layer of safety in operating procedures.

The other choices reflect actions that may not necessarily be required or appropriate before using a hand-operated dual control switch. While some may involve aspects of operation, stopping the train directly pertains to ensuring safety and proper procedure, making it the necessary step before proceeding.