cAMP, $IP_3$, and DAG are all molecules that are used as secondary messengers. Which statement below correctly identifies a difference between the pathways in which they are found?

• A. cAMP secondary messenger systems result in the activation of a kinase, while systems that use $IP_3$ and DAG do not.
• B. cAMP and $IP_3$ are part of the same signaling cascade, while DAG is found in different cascades.
• C. Adenylate cyclase produces cAMP while phospholipase C produces $IP_3$ and DAG.
• D. Both A & C are correct.