Final answer:
At a multiple track crossing, do not proceed until you are sure that all tracks are clear and there are no trains coming.
Step-by-step explanation:
When at a multiple track crossing, it is essential not to proceed until you can clearly see that all tracks are clear and there are no trains coming on any of the tracks. The question seems to be related to safety rules at a railway crossing, drawing a parallel to a situation when a river is flooded. In both scenarios, the advice is to wait for safe conditions. At a railway crossing, this would mean waiting until it is certain that there are no oncoming trains on any of the tracks before crossing to ensure safety.
Looking at the options provided, the correct response in the context of a multiple track crossing would be similar to option 'a', which states to stop moving and become stationary until it is safe to proceed. Safety is the priority, and the same principle of caution applies to both situations: flooded rivers and railway crossings.