Explanation:
Full Explanation:

To understand this, let’s break it down step by step:

What is the odontoid process?
- The odontoid process, also known as the dens, is a peg-like projection that sticks upward from the second cervical vertebra.
- Its main job is to pivot and allow the head to turn from side to side (as in saying "no").
Let’s look at the vertebrae options:

#A. Atlas (C1)
- This is the first cervical vertebra.
- It does NOT have an odontoid process.
- Instead, it is ring-like and supports the skull.
- It sits on top of the axis and rotates around the odontoid process of the axis.

#B. Axis (C2)
- This is the second cervical vertebra.
- It has the odontoid process (dens).
- The dens projects upward into the atlas, allowing the head to pivot.
- It’s a key part of neck movement.

#C. Thoracic vertebrae
- These are the mid-back vertebrae, connected to the ribs.
- They do not have an odontoid process.

#D. Lumbar vertebrae
- These are the lower back vertebrae.
- They are large and strong, built for weight-bearing, without any dens.

#E. Caudal vertebrae
- Found in the tail of some animals.
- Humans have a rudimentary version (coccyx), but no odontoid process.

Summary:
The Axis (C2) is the only vertebra with the odontoid process, which allows the Atlas (C1) and the skull to rotate.