Final answer:
Switching from walking to taking the bus results in a decreased activity level, as it replaces an active form of travel with a passive one.
Step-by-step explanation:
The question asks to identify which behavioral change results in a decreased activity level. When comparing the options, switching from walking to taking the bus represents a change from an active to a more passive mode of transportation, consequently decreasing the level of physical activity.
More workers are shifting from active work fields such as agriculture and manufacturing to service industries, where the physical demand is typically lower. Additionally, increased access to passive transportation, such as driving and taking the bus, correlates with people walking less and, therefore, being less physically active. This behavioral change in society can contribute to a range of health issues due to decreased physical activity levels.