Explanation:

- The layer of soil you are describing is dark, rich in humus and minerals, soft, porous, and retains water well.

- Option 1: B-horizon

- This is a subsurface layer called the subsoil.

- It contains minerals leached from the topsoil.

- It is generally lighter in color and denser.

- Option 2: Bedrock

- This is the solid rock beneath soil layers.

- It does not contain humus or minerals found in top layers.

- Option 3: C-horizon

- This consists of weathered rock and soil material.

- It is less affected by biological processes compared to topsoil.

- Option 4: Topsoil

- Topsoil is the uppermost layer of soil, rich in organic material.

- It is dark due to the presence of humus.

- It is soft, porous, and has high water retention.

Correct Answer: Option 4 - Topsoil