To determine the best combination of soils for plant growth, we need to analyze the options provided and understand the role of each soil component.
### Step-by-Step Solution:
1. **Identify the Components of Each Option**:
- Option A: Clay, Sand, Gravel
- Option B: Humus, Clay, Gravel
- Option C: Sand, Humus, Gravel
- Option D: Humus, Sand, Clay
2. **Understand the Importance of Each Component**:
- **Humus**: This is organic matter that improves soil fertility, enhances moisture retention, and provides essential nutrients for plants.
- **Sand**: Sand improves drainage and aeration in the soil, preventing compaction and allowing roots to breathe.
- **Clay**: Clay retains moisture and nutrients but can lead to poor drainage if present in excess.
3. **Evaluate Each Option**:
- **Option A (Clay, Sand, Gravel)**: Lacks humus, which is crucial for nutrient supply.
- **Option B (Humus, Clay, Gravel)**: Contains humus but may have poor drainage due to high clay content.
- **Option C (Sand, Humus, Gravel)**: Lacks clay, which may limit moisture retention.
- **Option D (Humus, Sand, Clay)**: This combination includes all three components, balancing moisture retention (from clay), drainage (from sand), and nutrient supply (from humus).
4. **Determine the Best Combination**:
- The best combination for plant growth is **Option D: Humus, Sand, and Clay**. This combination provides a balanced environment for plants, ensuring good drainage, moisture retention, and nutrient availability.
### Final Answer:
The best combination of soils for plant growth is **Option D: Humus, Sand, and Clay**.
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