<em>In my opinion, it would be C.</em> You never know how many calories this person has burned every day. In A and B, they specifically state how many miles each day. D could be like jogging for 10 minutes. But you never know how many calories answer C has.
The best form of exercise for weight loss is cardio, since it burns the energy stored in fat after a while of burning calories. In this case, the answer would be A. Cardio is an effective and fast way to burn fat, although a persons eating habits also directly influence weight.
So that you can help them or lead them in the right direction whether that be counseling or an adult. If they are depressed. Also because they could be using or turning to drugs which can also make them depressed or emotional.