Few places have so many versions of their origin as Stonehenge. People have suggested many ideas of its true purpose: an ancient (1) ________ (OBSERVE), a giant calendar, a place of pilgrimage, or even a landing site for UFOs. Experts, however, think Stonehenge was the centre of a ritual landscape. This idea fits with the many (2) ________ (BURY) places that surround the stone circle. The only thing we know for sure about Stonehenge is its age: construction began about 5,000 years ago and continued for (3) ________ (ROUGH) 1,600 years. Mount Rushmore is one of the world's largest stone sculptures. Finished in 1941, it shows four important American (4) ________ (PRESIDE) carved into the granite of South Dakota's Black Hills. The faces, from left to right as you look at them, are George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln. Each face is about 18 metres high.