Because it is flexible. Think about it; the ribs protect both the lungs and the heart. If the ribs were solid bone all the way around then unless you constantly break your ribs you wouldn't be able to expand the cheat to breath. Additionally your lungs would constrict the heart to a degree that it would function properly.
C. H<span>ow hard a person works to do an activity. Intensity has to do with effort. If a person works hard than they are intense, if vise versa than they are not intense.</span>
