Final answer:
Personal behaviors like picking the nose and scratching the scalp can contaminate hands, surfaces, and food.
Step-by-step explanation:
The personal behaviors mentioned in the question, such as picking the nose and scratching the scalp, can contaminate hands, surfaces, and food. When someone engages in these behaviors and then touches objects or food, they may transfer microbes from their skin or hair onto those surfaces, which can then be transmitted to other people.