The correct answer is: C. 8 kmph
The gross clearance is the minimum distance between the overhead power lines and the nearest part of the vehicle. The gross clearance is specified in millimeters (mm).
In electrified areas, the gross clearance must be at least 390 mm when the voltage is 25 kV AC. However, if the gross clearance is between 390 mm and 340 mm, the speed of the vehicle must be limited to 8 kmph. This is to ensure that there is enough clearance for the vehicle to pass safely under the overhead power lines.
Option A is incorrect because the speed limit is 8 kmph, not 10 kmph.
Option B is incorrect because the speed limit is 8 kmph, not 15 kmph.
Option D is incorrect because there is a correct answer.