Barnacles are pests of

Options

A. Crop plants
B. Fruit trees
C. Marine plants
D. Ships and hard shelled animals.

Answer

### Step-by-Step Solution:

1. **Understanding Barnacles**: Barnacles are crustaceans that attach themselves to various surfaces, including ships, rocks, and the shells of marine animals.

2. **Identifying the Options**: The question provides several options:
- Crop plants
- Fruit trees
- Marine plants
- Ships and hard-shelled animals

3. **Analyzing Each Option**:
- **Crop Plants**: Common pests of crop plants include insects like bollworms, not barnacles.
- **Fruit Trees**: Pests of fruit trees include species like the apple maggot, which do not include barnacles.
- **Marine Plants**: While barnacles may attach to marine plants, they are not typically considered pests of these plants.
- **Ships and Hard-Shelled Animals**: Barnacles are known to attach to the hulls of ships and the shells of hard-shelled marine animals like turtles and mollusks.

4. **Conclusion**: Based on the analysis, barnacles are primarily pests of ships and hard-shelled animals. Therefore, the correct answer is option number four.

### Final Answer:
Barnacles are pests of **ships and hard-shelled animals**.

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