empathy (noun):
ability to understand and share feelings of another
I believe the answer would be d.muscle cramps. Breathing in toxins seems like it could relate to the other three answers.
The adrenal gland releases adrenaline
working in the cardio will help to tone your abs and burn excess fat, and the respiratory system, with it being in good health from the exercise, your oxygen intake and the release of carbon monoxide will definitely increase and become steadier..