<span>B. Regular physical activity can help with energy levels, can improve self-image (and, thereby, school attendance), but it will not decrease a person's attention span. If anything, the person will increase their span because of the focus required to perform the activity to an acceptable level.</span>
I don't know, they all seem important. I think the basis here though is good eating habits.
When VOC's and nitrogen dioxide are acted by sunlight, the ozone is formed in the stratosphere. The amount of ozone present in our atmosphere is very significant to the climate on Earth. Ozone "shields" the Earth against the UV rays of the sun which could be hazardous to life on Earth.