I think it's B. Because if you're wearing something that filters oxygen (E.g. gas mask) and the substance becomes airborne, the filters in the protective gear might be overworked if the substance density is greater than the filtering capacity.
I think one thing you could do in order to measure your cardiovascular strength you can do a full sprint run. In order to help improve your fitness levels you can swim, jog/run, body weight exercises, and a balanced diet.
Lemons picked while still green will generally have a longer post harvest shelf-life than the fully yellow lemons that need to be handled gently and marketed more rapidly.
Hope this helps!! :))
I would decide one whether or not I want to keep doing this in my life and I would try to help out everyone I can