An advertisement uses words and pictures to     1     people to buy a product or service, or to believe in an idea. Newspapers, magazines, the Internet, radio and television are the most common places to find them. There are two main types of advertisements—commercial advertisements and public service advertisements (PSAs). A commercial advertisement is     2     which someone has paid for to advertise a product or service. PSAs are often run for free, and are meant to educate people about health, safety, or any other problem that affects public     3    .