The correct answer is: B. Main line set
A white light in a point indicator indicates that the main line is set. This means that the points are aligned so that a train can proceed on the main line.
A loop line is a secondary track that is used to allow trains to bypass a section of track that is blocked or under repair. A pass run through is a type of train movement that allows a train to pass through a station without stopping. All is right indicates that there are no problems with the track or the train.