What type of sand dune would most likely form if the sand supply is limited the wind direction is constant and vegetation is sparse?

The correct answer is - Barchan (barkhan) sand dune.

The barchan sand dunes can be seen all over the world where there's sand dominated deserts. They form when the wind is constant and blows from only one direction, thus making it look like a crescent. The part of the dune that faces the wind is longer and bigger, as well as having much less steeper slope, while the part of the dune that is sheltered from the wind becomes much steeper as the dune grows in size, and it also has two ''horns'' from each side.

20: 5

explanation:

about 20% of the world's population lives in   southwest asia, but on less than 5% of the world's   land area.