The correct answer is: The speed of the passenger train will not change when four wheeler is attached.
The speed of a train is determined by its engine and the weight of the train. The engine of a passenger train is designed to pull a certain amount of weight, and the weight of the train does not change when a four wheeler is attached. Therefore, the speed of the train will not change.
Option A is incorrect because the speed of the train is not limited to 80 km/h. The speed of the train is determined by its engine and the weight of the train, and the weight of the train does not change when a four wheeler is attached. Therefore, the speed of the train will not change.
Option B is incorrect because the speed of the train is not limited to 75 km/h. The speed of the train is determined by its engine and the weight of the train, and the weight of the train does not change when a four wheeler is attached. Therefore, the speed of the train will not change.
Option C is incorrect because the speed of the train is not limited to 85 km/h. The speed of the train is determined by its engine and the weight of the train, and the weight of the train does not change when a four wheeler is attached. Therefore, the speed of the train will not change.
Option D is incorrect because the speed of the train is not limited to 90 km/h. The speed of the train is determined by its engine and the weight of the train, and the weight of the train does not change when a four wheeler is attached. Therefore, the speed of the train will not change.