Corps of Engineers, Transportation Corps, Military Police...All Officers should have an appreciation of the ground they fight on, so your major is useful in almost every branch. In the Signal Corps many of the radio systems we use are line of sight. Being able to understand how the contour of the ground may effect communications is an application.
This seems like a really weird requirement for an ROTC class, since major and branch don't always correspond. I would suspect this exercise is more a way to get you to use effective briefing skills than a right/wrong answer on branch and major relationship.