The correct answer is D. Normal speed.
The speed of a train after normalized in OHE supply immediate after tripping is the normal speed of the train. This is because the train’s speed is controlled by the train’s traction control system, which is designed to maintain a constant speed regardless of the changes in the OHE supply.
The other options are incorrect because they are not the normal speed of the train. Option A is incorrect because it is the speed of a train after tripping when the OHE supply is not normalized. Option B is incorrect because it is the speed of a train after tripping when the OHE supply is normalized but the train’s traction control system is not working. Option C is incorrect because it is the speed of a train after tripping when the OHE supply is normalized and the train’s traction control system is working, but the train is going uphill.