The correct answer is A. Mitochondria.
Mitochondria are organelles that are found in almost all eukaryotic cells. They are responsible for producing energy for the cell in the form of ATP (adenosine triphosphate). ATP is a molecule that cells use to power their activities.
The cytoplasm is the jelly-like substance that fills the cell. It is made up of water, proteins, and other molecules. The cytoplasm does not produce energy for the cell.
Ribosomes are organelles that are responsible for protein synthesis. They do not produce energy for the cell.
Therefore, the correct answer is A. Mitochondria.