*Q:21 Correct Answer* ✅ *(1) Both A and R are true and R is the correct explanation of A* > *Explanation:* Cyclostomes (e.g., lampreys and hagfishes) are jawless vertebrates with a circular, sucker-like mouth adapted for sucking or rasping food, not for chewing. Their lack of jaws and the presence of a circular mouth are the reasons why they suck food rather than chew it.