Answer A because walking to school would take more effort and alertness but if you switch to riding the bus it doesn't take the same effort as it does walking
Switching from walking to taking the bus would mean a behavioral change that will result in a decrease in activity level. Whereas you were getting some form of physical activity in walking you are now taking the bus which means your level of physical activity has dropped as you will be sitting on the bus not doing anything, before you were actively moving your body.
