Final answer:
Muscle cells are primarily made up of water (73%), protein (24%), with smaller amounts of fat and carbohydrates for energy and structure.
Step-by-step explanation:
Muscle cells, also known as muscle fibers or myocytes, are primarily comprised of different substances that account for their function and structure. These muscle fibers are mainly made of protein, which is essential for their contracting ability. Also, water constitutes a significant portion of the muscle cell, followed by a limited amount of carbohydrates and fat within the muscle cell. The correct answer to the composition of muscle cells is a) Water (73%), Protein (24%), a limited amount of Fat with Carbohydrates in the muscle cell.