When the train catches fire, that carriage must be ________. A. Isolated B. Non-isolated C. Both D. None of these

Isolating the carriage will help to prevent the fire from spreading to other carriages, and will also help to protect the passengers and crew from the fire.

Option B is incorrect because a non-isolated carriage would allow the fire to spread to other carriages.

Option C is incorrect because both isolated and non-isolated carriages can catch fire.

Option D is incorrect because the carriage must be isolated to prevent the fire from spreading.