I would say C is the most correct.
In D it depends on what water source you're using. Let's say it is a waterfall, then the source of the water (melting ice or a lake) may disappear in the future.
If you're using underwater "windmills" placed in the ocean, then you would expect it to last a while as the ocean will not disappear in the near future.
Answer;
C. unchanged rock and mineral fragments
Explanation;
A large number of landforms and features found in desert environments are formed as the result of weathering. Weathering is defined as the breakdown and deposition of rocks by weather acting in situ
The two main types of weathering which occur in deserts are Mechanical weathering, which is the disintegration of a rock by mechanical forces that do not change the rock's chemical composition and Chemical weathering, which is the decomposition of a rock by the alteration of its chemical composition.
By contrast much of the weathered debris in deserts has resulted from mechanical weathering. Chemical weathering, however, is not completely absent in deserts. Over long time spans,clays and thin soils do form.
When calcium joins with calcium its follows the following equation:
2Ca + O2 = 2CaO
hope that helps
Question 5 is the second one.