The correct answer is: A. the gauge face of the stock rail and tongue rail.
The gauge face is the inside edge of the rail, and the tongue rail is the rail that is connected to the switch point. The switch angle is the angle between the gauge face of the stock rail and the tongue rail. This angle is important because it determines the direction that the train will travel when it enters the switch.
The other options are incorrect because they do not describe the correct relationship between the gauge face of the stock rail and the tongue rail. Option B describes the angle between the outer face of the stock rail and the tongue rail. Option C describes the angle between the gauge face of the stock rail and the outer face of the tongue rail. Option D describes the angle between the outer face of the stock rail and the gauge face of the tongue rail.
I hope this explanation is helpful. Please let me know if you have any other questions.