The correct answer is (a) parent rock from which soil is formed.
Explanation: Soil is primarily derived from the weathering and breakdown of parent rocks, which release minerals into the soil.
Why other options are incorrect:
(b) plants:
While plants absorb minerals from the soil, they are not the primary source of these minerals. Plants actually contribute organic matter to the soil through decomposition.
(c) animals:
Animals contribute nutrients to the soil through excrement and decomposition, but their primary role is not as a source of soil minerals.
(d) bacteria:
Bacteria play a crucial role in soil decomposition and nutrient cycling, but they do not directly provide the primary source of soil minerals.