Answer:
The correct answer would be d. mitochondria.
A mitochondrion is a membrane-bound cell organelle involved in the production of energy (ATP) for the cell.
The cardiac muscle or heart muscle is responsible for pumping blood throughout the body and thus, it works throughout life without rest.
The continuous contractions of cardiac muscle need more supply of ATP or energy as compared to any other cell of the body.
Thus, it has a high number of mitochondria so that its high energy demand can be fulfilled.
