Answer:
The correct answer is C (serve in WWI)
Step-by-step explanation:
Walter Camp was an American who was known/famous as a football player and coach and hence known as the "Father of American Football". He was a graduate of Yale college where he was a football player as a student and also became a coach of the college team (from 1888 to 1892).
He was once the manager of his family's clock company, the New Haven Clock Company. During world war I (WWI), as an adviser to the US military, he developed a method (of exercise known as the "daily dozen set-up") that assisted the US soldiers in keeping physically fit. He didn't however serve in the military as a soldier nor did he serve in the war. Hence, the correct answer is C.