Why might soils rich in organic matter not be fertile?
a.
soil fertility comes from a balance of organic matter and other mineral nutrients.
b.
large amounts of organic material make soil retain too little water.
c.
soil fertility is a result of the inorganic minerals present.
d.
soils rich in organic material are always highly fertile.

a. Soil fertility comes from a balance of organic matter and other mineral nutrients.

Explanation:

Soil fertility is the quality of soil which makes it suitable for the growth of the plants.

The fertility of the soil is not just dependent upon the organic matter present in the soil but also dependents upon the inorganic mineral content. The organic content increases the water holding capacity of soil which ensures that the plants get adequate moisture for their growth. Also, the inorganic minerals like calcium, potassium, nitrogen helps in different stages of growth and development in plants.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.