What is the first step in the cutting off and recouping airbrake test?

The correct answer is that the train is uncoupled and unchanged, as this is the foundational step in the cutting off and recouping airbrake test. This initial action ensures that the train's air brake system can be evaluated without interference from the rest of the train. By keeping the train unchanged, it allows for an accurate assessment of the brake performance on the specific set of cars being tested.

This step is critical because, during the airbrake test, it is necessary to isolate the portion of the train being tested to ensure that any issues observed are directly related to that section alone. Once the train is uncoupled and the setup is confirmed to be unchanged, subsequent steps can be performed to evaluate the functionality and responsiveness of the airbrake system, ensuring safety and operational efficiency.

The other options involve either actions that would be performed after this initial step or checks that would not provide the necessary isolation required for an accurate airbrake performance evaluation.