3) Choose the best answer. One of the benefits of diet and activity is an improved __ which helps the body fight contagious diseases. respiration system immune system digestion system

## Step 1<br />The question is asking us to identify the system in the body that benefits from diet and activity, which helps the body fight contagious diseases. The options given are the respiration system, the immune system, and the digestion system.<br />## Step 2<br />The respiration system is responsible for the intake of oxygen and the expulsion of carbon dioxide. While it is important for overall health, it is not directly responsible for fighting contagious diseases.<br />## Step 3<br />The digestion system is responsible for breaking down food and absorbing nutrients. While it is important for overall health, it is not directly responsible for fighting contagious diseases.<br />## Step 4<br />The immune system is responsible for protecting the body against harmful substances, including pathogens and diseases. It is the system that directly fights contagious diseases.<br />## Step 5<br />Therefore, the correct answer is the immune system.