Has anyone read A Separate Peace by John Knowles? If yes, then help

Why does Gene change his mind about enlisting in the military after he tells Brinker he will?

A) Gene thinks he is too young and is afraid of going to war.

B) Gene decides that if Finny can't enlist because of his leg, he won't either.

C) Gene realizes he made a foolish remark about enlisting.

D)Gene doesn't want to leave Devon because Finny has returned.