Deep inside a mountain near Sweetwater in East. Tennessee is a body of water known as the Lost Sea. It is listed by the Guinness Book of Would Records as the world’s largest underground lake. The Lost Sea is part of an extensive and historic cave system called Craighead Caverns.

　　The caverns have been known and used since the days of the Cherokee Indian nation. The cave expands into a series of huge rooms from a small opening on the side of the mountain. Approximately one mile from the entrance, in a room called “The Council Room,” many Indian artisfacts have been found. Some of the items discovered include pottery, arrowheads, weapons, and jewelry.

　　For many years there were persistent rumors of a large underground lake somewhere in a cave, but it was not discovered until 1905. In that year, a thirteen-year-old boy named Ben Sands crawled through a small opening three hundred feet underground. He found himself in a large cave half filled with water.

　　Today tourists visit the Lost Sea and ride far out onto it in glass-bottomed boats powered by electric motors. More than thirteen acres of water have been mapped out so far and still no end to the lake has been found. Even though teams of divers have tried to explore the Lost Sea, the full extent of it is still unknown.

　　66. The Lost Sea is unique because it is ________.

　　part of a historical cave system

　　the biggest underground lake in the world

　　listed in the Guinness Book of World Records

　　the largest body of water in Tennessee

　　67. The Craighead Caverns have been known ________.

　　A. through history B. since the time of the Indian nations

　　C. since 1905 D. since divers explored them

　　68. Who located the Lost Sea in recent times?

　　A. The Cherokee Indians. B. Tourists.

　　C. Ben Sands. D. Scientists.

　　69. What was found in “The Council Room”?

　　A. A small natural opening. B. A large cave.

　　C. Another series of rooms. D. Many old Indian objects.

　　70. It can be inferred from the passage that the Craighead Caverns presently serve as ____.

　　A. an underground testing site B. an Indian meeting ground

　　C. a tourist attraction D. a motor boat race course