rocks can become soil in multiple different ways one could be primary succession which means some algae or moss grows onto rocks with out soil then they slowly gain moisture which attracts some other plants like flowers which then breaks down the rock into smaller things then grasses come in and turns it into soil.
I would say oxygen because respiration is breathing mechanically.
Answer:
Design more studies testing the effect of duration and intensity of exercise on cholesterol levels in different age groups.
Explanation:
