Read the following excerpt, and then answer the following question.
"Allergies may seem similar to a cold, but the causes are very different. An allergy occurs when the body's immune system reacts to something the body contacts. How can you know if you have a cold or allergies? A short-term illness caused by contact with a virus is a cold. Allergies can't be spread from person to person and may last longer than a cold.
Neither allergies nor a cold are fun to experience, but understanding the differences can help you know how to respond."
Which format does the author use to help the reader understand the main idea?