George, who is 60, couldn't understand why he was slowly gaining weight. he was eating the same amount of food that he had each day since he was 20 and he exercised regularly. what could explain his weight gain?

a) his metabolism had slowed down.
b) he is likely very ill; this situation is very unusual.
c) he really wasn't gaining weight; his height was decreasing.
d) he always overate after exercising.