There are 12 pairs of rib bones and the last two are called floating ribs. Why is that the case:

• A. They articulate with the 10th ribs and attach to the sternum
• B. They are significantly shorter than the other rib bones but attach directly to the sternum
• C. The last two rib bones are fused
• D. They are short bones that do not attach to the sternum

Answer: (D)