It is known as a concentration gradient which in diffusion will always flow from ares of high concentration to areas of low concentrations
So i believe the answer to this is A.
In order to study the formation of cancer cells, you should study the life cycle of normal cells as cancer cells are abnormal cells.
Actually, Normal cells grow, divides and died after an interval of time. And when this process is break down, cancer cells begin to form. They are usually old cells which don't die after their life cycle.
Hope this helps!
Biotic Factors are any living components that affect other organisms, and since soil is not alive (soil is an abiotic factor) then you can eliminate A., B., and C. D is the answer choice that has only biotic examples.
