The correct answer is: C. head of rail.
A fish plate is a metal plate that is used to fasten two rails together. It is placed between the rails and is secured in place with bolts or spikes. The fish plate is in contact with the head of the rail, which is the top surface of the rail. The head of the rail is the part of the rail that bears the weight of the train.
The web of the rail is the vertical part of the rail that connects the head of the rail to the foot of the rail. The foot of the rail is the bottom surface of the rail. The foot of the rail rests on the ballast, which is the material that supports the rails.
The fishing plane is a flat surface on the fish plate that mates with the head of the rail. The fishing plane helps to distribute the load evenly across the rail and prevents the rail from derailing.