How can parking brakes be applied?

The correct answer is the option that allows parking brakes to be applied from any engineer's cab with an active master controller. This functionality is crucial for train operations, as it provides the flexibility needed for the engineer to engage the parking brakes from different locations on the train.

When an engineer is in control, having the ability to apply the parking brakes from their cab ensures they can respond quickly to various situations, such as preparing the train for a station stop or securing the train in the event of an emergency. This adaptability is particularly important in scenarios where immediate action is required to prevent unintended movement, thereby enhancing operational safety.

In contrast, other methods of application described in different options either limit the accessibility of the parking brakes or do not reflect the operational procedures followed in train management. For instance, applying the parking brake only from a control center would reduce the responsiveness of the crew in emergency situations, while a requirement for manual application could lead to safety concerns, especially if conditions necessitate rapid engagement of the brakes. Automatic application when the train stops may not adequately account for all stopping scenarios, which requires engineer intervention to ensure safety and operational efficiency.