7. What is the passage mainly about?
When the Spanish Conquistadors, or "conquerors," visited Central America in the 16th Century, they had a rare opportunity to watch the Aztec people play an unusual ballgame. On a narrow field surrounded by stone walls, two teams passed a hard rubber ball back and forth. The objective was to keep the ball in the air. If a player let the ball bounce twice before passing it to the other team, he or she lost a point. Though the Conquistadors didn't know it at the time, the game they were watching had been around for thousands of years. In fact, modern-day archaeologists have discovered ancient stone courts and rubber balls throughout Central America. Some of these discoveries date as far back as 1400 B.C.! The ball courts vary considerably in size, but most have the following characteristic in common: long narrow alleys with stone side-walls against which the rubber balls could bounce. The game seems to have originated in Southern Mexico, where rubber trees were plentiful. While the rules of the ballgame are a mystery to us today, it's a good bet that the game was similar to volleyball, where the aim is to keep the ball in play. In the most widespread version of the game, players could only use their hips to hit the ball back and forth. In later years, a vertical stone ring was added to the ball courts as an additional way to score points, making the game similar to basketball. Other variations of the game permitted using forearms, rackets, or bats to hit the ball back and forth. Thankfully, the game has not been entirely forgotten. A modern version of the game, called ulama, is still played in a few places in Mexico by the local indigenous population.

7. What is the passage mainly about?
a. The object of the Aztec game was to pass the ball without letting it drop.
b. The Aztec people played a game similar to volleyball for thousands of years.
c. After years of study, archeologists have learned the rules of a game called ulama.
d. Balls made from rubber trees have been discovered in Southern Mexico.