Question

What has hot days and cool nights, and are typically covered with sand dunes or sparse but hardy plants?

Answer 1

deserts

The driest climates are deserts . Most occur between about 15 and 30 latitude. This is where dry air sinks to the surface in the global circulation cells. Deserts receive less than 25 centimeters  10 inches  of rain per year. They may be covered with sand dunes or be home to sparse but hardy plants  see Figure below  . With few clouds, deserts have hot days and cool nights.