Sean began jogging to live a healthier lifestyle. On his first run, he ran one-half mile. He increased his workouts by adding two miles a month to his run. He wrote the equation f(x)= 0.5 + 2x to model his progress. The variable x represents the number of?

Amiles he runs.

Bmonths he runs.

Cmiles he ran the first day.

Dcalories he burns.