Which of the following soils has the minimum humus content?

Grey desert soil is also called sierozem and it is the typical soil of the mid-latitude desert regions. Due to lack of the natural vegetation in these regions of dry climate, the grey desert soil is phenomenally poor in humus. Red desert soil is a characteristic of still more arid regions, and their colour ranges from pale reddish grey to deep red. The humus content reaches its lowest possible limits and the role of plants as soil formers is also reduced to the minimum. Chernozem soil is the most widespread among all zonal soils of the semi-arid climate. It is rich in humus. Chestnut soil lies on the arid side of the chernozem soils. It is lighter in colour and contains less amount of humus.