Final answer:
Hand washing is the most effective action to prevent the spread of contagious illnesses by reducing the number of microbes on surfaces and hands.
Step-by-step explanation:
Hand washing is the most effective action to prevent the spread of contagious illnesses.
Microbes, which are tiny organisms that can only be seen with microscopes, are found on various surfaces and can enter the body through contact with hands.
Washing hands can remove these microbes and reduce the risk of infection.
For example, if someone sneezes into their hand and then touches a doorknob, the microbes from their sneeze can be transferred to the doorknob and then to another person's hands.
If that person then touches their mouth, nose, or eyes, the microbes can enter their body and potentially cause illness.