Carlsbad Caverns National Park contains more than 100 caves below the surface of the desert. Most are     1     to the public. But anyone can visit the main     2     , one of the largest caves in the world.

An elevator lowers you into the world of Carlsbad Cavern. It is really long     3     of chambers. One of these is called the Big room. It is more than three hectares big and the ceiling is 77 meters high. The Big Room is the     4     largest underground chamber ever found in North America.

The Big Room and other parts of the cavern contain huge, sharp formations of minerals. People are     5     to explore the lit formations in the Big Room. But park rangers must guide visitors to other areas of the cave.

Stalactites(钟乳石)hang from the     6     . Stalagmites(石笋)rise from the floor. Some even meet to create a column. Other formations look like needles, popcorn, pearls and flowers.

One of the first questions that visitors have is 'how did Carlsbad Cavern form? ' Guides explain that it did not result from the action of water and streams like other limestone caves. Instead, it was     7     by the action of sulfuric acid(硫酸).

People are not the only ones who visit Carlsbad Caverns National Park. About 400,000 Mexican free-tailed bats come to the big cave from Mexico each summer to give     8     .

It is easy to imagine that it was the bats that     9     ancient people to discover the cave. Archeologists and others have found     10     of Ice Age hunters near the cave entrance. They have also found pieces of spear(矛) points left about ten thousand years ago.