The answer is C. influenza, chicken pox, and colds because influenza, chicken pox, and colds (called rhinovirus) are all caused by viruses. Food poisoning is not a virus, athlete's foot is a fungal infection, and strep throat is a bacterial infection.
There are many websites you can visit however, the following link is a good one. https://www.cancer.gov/about-cancer/understanding/what-is-cancer
When we are little we see the way our parents or elders act and that tells our brain that is the correct way to act. As we grow up the things they tell us we will become is what we think will happen and so we do that in fear that we will disappoint them.