Which behavioral change results in a decreased activity level?
switching from walking to taking the bus
switching from driving to taking the train
switching from taking the bus to walking
switching from taking the train to taking the bus

The correct answer is A.

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.