What action must be taken if air leakage exceeds the maximum amount during testing?

Answer: A — The train must be inspected for leakage.

When air leakage during testing exceeds the maximum allowable amount, it is crucial to inspect the train for leakage. This action is necessary because excess air leakage can indicate damage or failure in the air brake system, potentially leading to improper braking performance. The integrity of the air brake system is vital for safe train operation, and any significant loss of air pressure could compromise the effectiveness of the brakes. By inspecting the train, technicians can identify and repair any faulty components, ensuring that the air brake system functions correctly and safely before the train continues its operation. The other options suggest actions that either do not directly address the issue of excessive leakage or imply that the system is functioning correctly when it is not, which could endanger safety.