The correct answer is: C. both (a) and (b).
The largest dune fields in the world are found in the Sahara Desert in North Africa and the Arabian Desert in the Middle East. These deserts are home to some of the largest and most impressive sand dunes on Earth. The dunes in these deserts can reach heights of over 100 meters (330 feet) and can stretch for hundreds of kilometers (miles).
The Sahara Desert is the largest hot desert in the world, covering an area of over 9 million square kilometers (3.5 million square miles). The Arabian Desert is the second largest hot desert in the world, covering an area of over 3 million square kilometers (1.2 million square miles).
Both the Sahara Desert and the Arabian Desert are located in arid regions with very little rainfall. The lack of rainfall means that there is very little vegetation in these deserts, which allows the sand to be blown by the wind and form dunes.
The dunes in the Sahara Desert and the Arabian Desert are constantly changing shape and size due to the wind. The wind blows the sand from one place to another, and the dunes are constantly shifting and moving.
The dunes in the Sahara Desert and the Arabian Desert are a popular tourist destination. People come from all over the world to see these amazing sand dunes.