The correct answer is: A. Outermost signal.
A station limit is the portion of a railway track between the outermost signal and the stop marker. The outermost signal is the signal that indicates the end of the section of track that is under the control of the signaller. The stop marker is a physical marker that indicates the end of the station platform.
The station limit is important because it defines the area where trains are allowed to operate. It is also important because it helps to ensure the safety of passengers and staff.
Option B is incorrect because the innermost signal is not part of the station limit. The innermost signal is the signal that indicates the beginning of the section of track that is under the control of the signaller.
Option C is incorrect because both the outermost signal and the innermost signal are not part of the station limit. The station limit is the portion of track between the outermost signal and the stop marker.
Option D is incorrect because the station limit is a real and defined area. It is not a hypothetical or theoretical area.