Which habit would most likely improve the health of your lungs?
smoking cigarettes in social situations

holding your breath in regular intervals

eating foods that are high in fat and sugar

engaging in moderate amounts physical activity

Engaging in moderate amounts of physical activity is the correct answer. 
Although the research is not yet final, some findings suggest that you risk of lung cancer may be lower if you get regular physical activity (compared to people who are not active.)

engaging in moderate amounts physical activity