Final answer:
The ribs known as floating ribs are the 11th and 12th pairs, which do not have anterior attachment, making them free at their ventral ends.The correct option is C.
Step-by-step explanation:
The ribs that are attached posteriorly to the thoracic vertebrae but are not attached anteriorly are known as floating ribs (answer C). These ribs are the 11th and 12th pairs of ribs, which are not attached to the sternum or to the costal cartilage of another rib
Floating ribs are classified as false ribs, along with the 8th to 10th ribs, which are connected indirectly to the sternum via the cartilage of the rib above them.
However, only the last two pairs, the 11th and 12th, are considered floating because they do not have any anterior attachment, thus 'floating' freely at their ventral ends.The correct option is C.