Some dances gain more popularity than others because they can be performed to different kinds of music and the steps change accordingly. One such dance is waltz .     There is a basic form for waltz, which you can see in this drawing of a dancing couple. The man places one arm around the woman's waist and she places her opposite hand on his shoulder. Then, they stretch their other arms out from their bodies and clasp hand. If someone tries to teach you a formal kind of dancing, chances are your teacher will start with the waltz. Have you ever tried to dance like this?      There are lots of different kinds of waltz, all performed to different types of waltz music.  The music might be fast or slow but what they all have is a regular one-two-three, one-two-three rhythm.   The traditional form is the old-school waltz in which dancers turn all the time with a hopping , springy step. This waltz has a slow, smooth, gliding step. There's also the Mexican waltz, which moves much faster. Listen to this Mexican waltz music and you can imagine how fast the dancers had to move.     Formal dancing has even become a profession, with people entering competitions. Have you ever seen a formal dance competition?     Today, ballroom dancing is almost considered a competitive sport; professionals perform different dances, each with strict rules. Everything from where the dancers place their hands to how they move is judged. In the glide waltz, dancers are judged by how smoothly they move. " I can dance with a glass of water on my head," is a well known sentence used by skilled dancers in the old days. In the past, some people learned how to dance by reading books, while others studied with a teacher called the "dancing master." How do people learn to dance today? What is the author's purpose in writing the passage?
To tell us to learn waltz. To tell us how to dance. To tell us something about waltz. To tell us the development of waltz.