Deserts form in places where air masses are usually a cold b expanding c falling d rising e humid?

Deserts are regions that receive very little precipitation. When air expands, it cools and its ability to hold water vapor decreases. This causes the water vapor to condense and form clouds. When the clouds become saturated, the water vapor falls as precipitation. However, if the air is too cold, the water vapor will not condense and form clouds. This is why deserts are often found in areas where the air is cold and dry.