Rewrite the following sentences, choosing the right word from those given in brackets :

1.  (Humus / Regolith) is produced by the decayed organic material, including dead leaves, stems roots, living bacteria, fungi, worms and other organisms. 

2. (Weathering / Denudation) refers to the gradual disintegration and decomposition of rocks which lie exposed to the elements of weather. 

3. (Young / Mature) soils are those which are undisturbed by erosion or deposition. 

4. (Hydration / Carbonation) occurs when the water itself combines chemically with some element or mineral. 

5. (Oxidation / Solution) is the chemical process in which some of the minerals are dissolved by the water.