Which of the following sentences expresses the main idea of the article?
Pickleball is a unique sport that combines parts of several sports, and it is growing in popularity.
Pickleball is often played in parks, but it's also played by residents in retirement communities.
Pickleball games are competitive, and players win points by hitting the ball over a net before it bounces twice.
Pickleball players must steer clear of the non-volley zone, but that can be very difficult at times.