When a portion of a train is left in a block section, ________ Must be shown on the front vehicle of the rear portion of the train during night. A. Red Light B. Green Light C. Both D. None of these

The correct answer is: A. Red Light

A red light must be shown on the front vehicle of the rear portion of the train during night. This is to ensure that other trains are aware that there is a train stopped ahead and to prevent collisions.

The other options are incorrect because they do not meet the requirements of the question. A green light is not required to be shown on the front vehicle of the rear portion of the train during night. In fact, a green light could be confusing to other trains, as it could be interpreted as a signal to proceed. Both a red light and a green light are not required to be shown on the front vehicle of the rear portion of the train during night. Only a red light is required.