Biology

The correct answer is: A.Rocks.

Phosphorus primarily exists in the Earth's rocks, especially in the form of phosphate minerals. These minerals are found in large quantities in sedimentary rock formations, which are the largest natural reservoir of phosphorus. Phosphorus is released into the environment through processes like weathering and erosion of these rocks.

Here's a breakdown:

A.Rocks: Phosphorus is most abundant in rocks as phosphate minerals (e.g., apatite). Over geological timescales, weathering of these rocks relea...