________ help the bones to move at the joints.

Answer

Step-by-Step Solution:

1. **Understanding the Question**: The question asks what helps bones to move at the joints.

2. **Identifying the Components**: Bones alone cannot move; they require assistance from another structure to facilitate movement.

3. **Recognizing the Role of Muscles**: Muscles are the structures that are attached to bones. They play a crucial role in the movement of bones at the joints.

4. **Explaining Muscle Function**: Muscles work through two main actions: contraction and relaxation.
- **Contraction**: When a muscle contracts, it pulls on the bone, causing movement.
- **Relaxation**: When a muscle relaxes, it allows the bone to return to its original position.

5. **Conclusion**: Therefore, muscles are essential for enabling the movement of bones at the joints.

6. **Final Answer**: The correct answer to fill in the blank is "muscles".

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