Pick the odd one out.
Biceps, triceps, diaphragm, knee cap.

Explanation

To solve the question of picking the odd one out from the options: Biceps, Triceps, Diaphragm, and Knee Cap, we can follow these steps:

### Step 1: Identify the nature of each option
- **Biceps**: A muscle located in the upper arm that helps in arm movement.
- **Triceps**: Another muscle located in the upper arm that works with the biceps to facilitate arm movement.
- **Diaphragm**: A muscle that separates the chest cavity from the abdominal cavity and plays a crucial role in breathing.
- **Knee Cap**: A bone, specifically known as the patella, that protects the knee joint and aids in movement.

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