The correct answer is C. 10 km/h.
The SE (P.way) is the Senior Electrical (Permanent Way) Inspector. They are responsible for the safety of the railway track and its infrastructure. If the SE (P.way) is not with the train, then the maximum speed at the spot of lurch shall be 10 km/h. This is because the SE (P.way) is the only person who can assess the safety of the track and give permission for the train to proceed at a higher speed.
Option A is incorrect because 15 km/h is too fast for a train to travel if the SE (P.way) is not with the train. The track may not be safe and the train could derail.
Option B is incorrect because 20 km/h is still too fast for a train to travel if the SE (P.way) is not with the train. The track may not be safe and the train could derail.
Option D is incorrect because 25 km/h is definitely too fast for a train to travel if the SE (P.way) is not with the train. The track may not be safe and the train could derail.