Sentence Completion

Complete the sentence with ONE word from the passage for each blank.

The Sahara was not always a desert. Around eight thousand years ago, much of it was covered in grassland dotted with lakes, and herds of animals roamed where sand now lies. Rock paintings left by people of that time show hippos and cattle in places that are bone-dry today. A slow shift in the planet's tilt gradually reduced the rainfall, and the green landscape turned to sand over many generations.

Thousands of years ago the Sahara was covered in , and ancient rock still show animals that needed water.