I would say the best answer would be A. oxygen deficit because it occurs at the beginning stages of your exercise.
EPOC is a measurably increased rate of oxygen intake following strenuous activity. So it can't be B.
In a steady state, it occurs mid workout, starting at about 10 to 15 minutes for beginners and 20 to 90 minutes for more fit athletes. So it can't be C.
It definitely can't be D. either because the resting heart rate is taken after you workout.
So, your answer will be A. oxygen deficit.
Hope I helped :)
