The example of pivot joint is

Options

A. Hip joints
B. Metacarpophalangeal joints
C. Ankle joints
D. Radioulnar joints

Answer

### Step-by-Step Solution:

1. **Understanding Pivot Joints**: A pivot joint allows for rotational movement. In this type of joint, one bone has a cylindrical shape, and the other bone forms a ring around it. This structure enables the first bone to rotate within the ring of the second bone.

2. **Analyzing the Options**:
- **Option A: Hip Joint**: The hip joint is a ball-and-socket joint, which allows for a wide range of movements, but it is not a pivot joint.
- **Option B: Metacarpophalangeal Joint**: This joint is an ellipsoid joint, allowing movement in two planes but not rotational movement characteristic of pivot joints.
- **Option C: Ankle Joint**: The ankle joint is a hinge joint, which permits movement in one plane (flexion and extension) but does not allow for rotation.
- **Option D: Radio-Ulnar Joint**: This joint is a classic example of a pivot joint. The radius has a cylindrical shape, and the ulna forms a ring around it, allowing for rotational movement (e.g., turning the palm up and down).

3. **Conclusion**: After analyzing all the options, the correct answer is **Option D: Radio-Ulnar Joint**, as it exemplifies the characteristics of a pivot joint.