Three divers enter a hole leading to a water-filled cave on Mexico's Yucatan Peninsula. They swim for an hour. Finally, they reach a large room 60 feet underground and about the size of two basketball courts. Here, they discover an upside-down human skull. Other bones lie nearby.

The team came across the skull in 2007. The divers then told the Mexican government about the finding. Soon the government formed a team of scientists to look into it. The group, which included archaeologist Dominique Rissolo, believed that the skull belonged to someone who lived in the last ice age. At the ice age some twenty thousand years ago, sea levels dropped and new land appeared. Over time, rain and wind ate holes into some of the land.

"The person may have died after entering the cave," Rissolo says. Then, when the ice age ended some ten thousand years ago, sea levels rose. Water flooded the cave, covering the remains.

Worrying that moving the skull might destroy it, scientists decided to examine it at its watery resting place. They collected information about the skull and other pieces of bones. They found that the bones belonged to a 15- to 17-year-old girl who lived at least twelve thousand years ago. The team named her after a type of water nymph (仙女) in Greek myths: the Naiads (Naia).

Naia is the oldest nearly complete human skeleton (骨架) ever found in the Americas. DNA tests showed that she's a direct ancestor of present-day Native Americans. Naia's DNA also matches with people native to Siberia, a part of Russia. Scientists have long thought that ancient people from this area arrived in Alaska during the last ice age. They were the first humans to live in the Americas. And Naia proves how far south they went.

In 2014 the scientists decided to bring up Naia's skull from the cave to protect it from curious divers. So it was taken to a lab, where it remains today.

【小题1】What can we learn about the skull?

A．It was left alone in the cave.

B．It lay under a basketball court.

C．It drew the government's attention.

D．It was discovered by three scientists.

【小题2】Why was the skull studied in the cave?

A．Scientists tried to protect it.

B．The temperature was fine in there.

C．It was against the law to take it out.

D．It would help scientists study the cave.

【小题3】Who were Naia's distant ancestors?

A．Early humans in Greece.

B．Early humans in Siberia.

C．Early humans in Alaska.

D．Early humans in Mexico.