Which of the following blood vessels is unpaired?

• A. Jugular vein.
• B. Common carotid artery.
• C. Azygos vein.
• D. Common iliac artery.
• E. Popliteal artery.
• F. Subclavian vein.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of paired vs. unpaired blood vessels. Paired vessels are those that have a counterpart on the opposite side of the body, while unpaired vessels are single and located along the midline without a duplicate.
2. Step 2: Review each blood vessel option to determine if it typically exists as a pair or a single vessel in human anatomy.
3. Step 3: Jugular veins, common carotid arteries, common iliac arteries, popliteal arteries, and subclavian veins are all paired vessels because they appear on both the left and right sides of the body.
4. Step 4: The azygos vein is an unpaired vessel that runs along the right side of the vertebral column and collects blood from the thoracic wall and upper lumbar region, draining into the superior vena cava.
5. Step 5: Conclude that among the options, the azygos vein is the only unpaired blood vessel, making it the correct answer.