When your body burns calories more efficiently, you
a. exercise without fatigue.
b. decrease the amount of muscle mass and increase the amount of body fat.
c. lose all your body fat.
d. increase the amount of muscle mass and decrease the amount of body fat

I think its D, I say this because when you work out, you burn calories because your body is busy doing something for a long period of time. You gain more muscles in your legs, and don't gain weight because that would be like eating a tub of ice cream in 10 minutes and expecting, that you would loose 10 pounds... No... Hoped I helped you out!