The correct answer is: A. 25/10 km/h
The speed of the engine shall be 10 km/h when entering the obstructed block section T/A 602. This is because the section is obstructed and the engine must proceed with caution. The authority to send the assisting engine into the obstructed block section is issued by the train dispatcher.
Option B is incorrect because the speed of the engine shall be 10 km/h, not 20 km/h.
Option C is incorrect because the speed of the engine shall be 10 km/h, not 15 km/h.
Option D is incorrect because the speed of the engine shall be 10 km/h, not 0 km/h.