Read this excerpt from "Herd about the Flu." Herd about the Flu

It's winter and the flu is raging. It's in your school, you know people who have caught it, and you are washing your hands for the fifth time. Missing school because of flu might not sound so bad, but the flu is one of the worst viruses you can have. The chills, the fever, the severe aches in your legs and arms . . . It's not something you want. Your mom drives you to the drugstore and you see a sign: No Flu Shots Available.

Wait a minute—there is a bad flu this season. You need the shot.

Where is the shot, and why can't you get it?

There are several answers to these questions. First, it just may not be ready. Flu viruses change all of the time, so new flu vaccines must be produced every year, and they take months to develop in research labs.

What is the purpose of the lines that are underlined?

These are answers to topic questions, and the paragraphs after them explain the answers.
These are summary points so that the reader could just read these lines and understand the passage.
These are conclusions that summarize all of the information in the paragraphs before them.
These are headings that give titles to the topics being discussed in the paragraphs after them.