The correct answer is B. web.
The web is the central part of the rail, between the head and the foot. It is the longest and widest part of the rail, and it is responsible for carrying the weight of the train. The head is the top part of the rail, and it is responsible for guiding the train. The foot is the bottom part of the rail, and it is responsible for keeping the rail in place on the track.
The web is the strongest part of the rail, and it is the part that is most likely to fail. If the web fails, the rail can break, and this can cause a derailment. Therefore, it is important to ensure that the web is made of high-quality material and that it is properly maintained.
The head and foot of the rail are also important, but they are not as critical as the web. The head is responsible for guiding the train, and the foot is responsible for keeping the rail in place on the track. However, if the head or foot fails, the train can still travel safely.
Therefore, the largest percentage of material in the rail is in its web. The web is the strongest part of the rail, and it is the part that is most likely to fail. If the web fails, the rail can break, and this can cause a derailment. Therefore, it is important to ensure that the web is made of high-quality material and that it is properly maintained.