Which of the following must be done before making a trailing movement through a spring switch?

Before making a trailing movement through a spring switch, it is imperative to ensure that the switch is properly lined by hand. Spring switches are designed to automatically align to one side or the other based on the direction of approach. However, when making a trailing movement, it becomes crucial that the switch is in the correct position to avoid accidents.

By lining the switch by hand, you verify that it is set to the desired route, preventing potential derailment or other safety hazards that could occur if the switch is inadvertently set for a different route. This step prioritizes safety by ensuring that the switch is configured correctly for the movement being made.

Other actions such as performing a visual inspection or controlling speed are important safety practices too, but they do not directly address the critical requirement of ensuring the switch's alignment for a trailing movement. Shouting a warning is also helpful for alerting others of the movement, but it does not ensure the safety of the switch itself. Thus, lining the switch by hand is a fundamental step that must take precedence before proceeding.