Soil science terminology: identify the correct statements about soil profile, horizons, and transitional boundaries between horizons.

Introduction / Context:
Basic pedology (soil science) uses standard terms to describe how soil varies with depth. Examinations often test recognition of the soil profile, its layers (horizons), and the nature of their transitions (boundaries), which are critical for land capability, agriculture, and geotechnical interpretations.

Given Data / Assumptions:

• A vertical cut through soil into parent material reveals distinct layers.
• Layers broadly parallel to the ground surface are termed horizons (e.g., O, A, E, B, C, R).
• The interface transition between horizons is termed the boundary.

Concept / Approach:
The soil profile is the entire vertical sequence from topsoil to parent material; horizons are diagnostic layers with characteristic colour, structure, texture, and chemistry; boundaries describe how sharply or gradually properties change across interfaces.

Step-by-Step Solution:
Confirm 'profile': full vertical section into parent material.Confirm 'horizons': layers roughly parallel to surface with distinct properties.Confirm 'boundary': the transitional zone between two horizons (abrupt, clear, gradual, diffuse).Since all are standard definitions, choose the inclusive option.

Verification / Alternative check:
Soil taxonomy manuals and pedology texts employ these exact terms.

Why Other Options Are Wrong:

• Each single statement is correct; excluding any would be incomplete.

Common Pitfalls:

• Confusing a single horizon with the entire profile.
• Overlooking that boundaries can be wavy, smooth, or irregular and vary in distinctness.

Final Answer:
All of these