Carol Shepard, age 9, of Shreveport, La., for her question:

WHERE IS THE WORLD'S LARGEST DESERT?

Stretching across North Africa from the Atlantic Ocean to the

Red Sea, and from the Mediterranean Sea to the Sudan is the Sahara Desert. It is the largest desert in the world.  It is hard to believe, but the Sahara is almost as large as the entire United States. The desert covers about 3 million square miles. Its greatest length, measured from east to west, is about 3,200 miles, or a greater distance than from San Francisco, Calif., to New York City. The desert is from 800 to 1,400 miles wide from north to south.

Most of Algeria, Libya and Egypt is covered by the Sahara and parts of Morocco, Tunisia and the Sudan are too. The desert also extends into Chad, Niger, Mauritania, Mali and Western Sahara.

Parts of the Sahara are covered with hot, shifting sand dunes while other parts have hard, rocky surfaces.