Final answer:
Part A is the mitochondria, Part B is the nucleus, Part C is the Golgi apparatus, and Part D is the ribosomes.
Step-by-step explanation:
Part A is the mitochondria, which is a bean-shaped structure with folds inside and is known as the powerhouse of the cell.
Part B is the nucleus, which is the round central structure and contains the cell's genetic material.
Part C is the Golgi apparatus, which is made up of flattened sacs and is involved in packaging and sorting proteins for transport.
Part D is the ribosomes, which are small round structures in the cytoplasm and attached to the nucleolus. Ribosomes are involved in protein synthesis.