Final answer:
Compound A most likely contains proteins, since proteins are abundant in meats and muscles and are essential for muscle structure and function.
Step-by-step explanation:
The macromolecule most likely present in compound A, which is found in large quantities in meats and muscles, is proteins. Muscles are made up of proteins, which serve as the primary structural and functional molecules in muscle cells. The four major classes of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids, with proteins being a key component of muscle tissue. Furthermore, proteins and lipids are the main components of myelin, another tissue associated with the nervous system.