Commissioned for Army or Marines?

Im about to start Army JROTC at highschool and plan to do it to better myself and get better and prepared for the Army. Well my step--dad dislikes the idea of me doing army and would prefer me to join the airforce or navy. Ive decided I'm doing army and have no wish to do the navy or airforce. I scored rather high on my PSATs so my step-dad went online and got me an oregon university package since we will be moving there in 3 years(atleast my parents will). He mentioned that it has Marines ROTC and that all the ROTCs allow you to be an officer for any branch. Is this true?