Deserts of Australia covers the 1,371,000 square kilometres which are 18% of the Australian mainland. But, approximately 35% of the Australian continent receives very low rain. So, it is effectively desert. In Australia, deserts are primarily distributed throughout the western plateau and interior lowlands of the country.
The main reason for this deserts is its location. Like most major deserts across the world, they are found around a certain latitude where the weather phenomena create a dry climate. So, Australian desert covers about 35% of that continent. Thus the correct option is D.