When you imagine a desert, what do you see? If you are like most people, you probably picture sand, sand, and more sand. But did you know that only one-fifth of the world's largest non-polar desert, the Sahara, is covered by sand? The rest of the 3.5 million square miles of the desert, in Africa, is made up of rock and rubble. Most people think the Sahara is covered by sand because of the many pictures of the sand dunes of the desert. The sand dunes are very expansive—they measure over one hundred miles wide and two hundred feet tall. These great sand dunes, called whalebacks, are what photographers and filmmakers focus on when they film the Sahara. So, naturally, the image of the Sahara as a sand-covered wasteland is what most people picture.

Which of the following best summarizes this paragraph?
A.
The sand dunes of the Sahara are called whalebacks. They are called this because they look like the backs of whales barely peeking out from the ocean.
B.
The Sahara Desert is the largest hot desert in the world. It is over 3.5 million square miles large, and people usually picture it as a sand-covered wasteland.
C.
The Sahara Desert is an interesting place to photograph. Photographers and filmmakers especially like to focus on the hundreds of miles of sand dunes.
D.
Many people think the Sahara Desert is covered by sand, but it is not. The Sahara is made mostly of rock and rubble, though it has hundreds of miles of sand dunes.