The correct answer is: A. S&T (T/351)
A point indicator is a device that shows the position of a railway point. It is typically a light that is either green or red, depending on whether the point is set for the main line or the loop line.
When the points are set for the loop line, the point indicator will show a green light. This is because the loop line is a secondary line that is used for trains that are not going to the main station. The green light indicates that the train can proceed onto the loop line.
When the points are set for the main line, the point indicator will show a red light. This is because the main line is the primary line that is used for trains that are going to the main station. The red light indicates that the train must stop before proceeding onto the main line.
The other options are incorrect because they do not correspond to the correct light that is shown by a point indicator when the points are set for the loop line.