3) add information that further explains or defines the main idea.
Extension mean to add on to, so 3) is the correct answer.
Answer:
“Quora - A Place to Share Knowledge and Better Understand the World.” <em>What Happens to the Planets When a Star Dies?</em> - Quora, www.quora.com/.
An informed opinion is based on knowledge of the facts and carefully considered principles. It relies on evidence instead of limited personal experience.
When you choose sources for your papers, you will generally want an informed opinion from a professional source.
If a reporter summarizes a study or quotes an expert, try to find the original source. Generally the original source is considered the most reliable: it's the most complete and you can judge the evidence for yourself.