Correct!

Your car breaks down on a level crossing. What's the first thing you should do?

Tell drivers behind what's happened
Leave your vehicle and get everyone clear
Correct answer
Walk down the track and signal the next train
Stay in your car until you're told to move

DVSA theory test explanation

If your vehicle breaks down on a level crossing, your first priority is to get everyone out of the vehicle and clear of the crossing. Then use the railway telephone, if there is one, to tell the signal operator. If you have time before the train arrives, move the vehicle clear of the crossing, but only do this if the alarm signals are not activated.