Solution

Ribosomes are often referred to as the engines of the cell. RNA is the most abundant substance of ribosomes. They are composed of proteins and ribosomal RNA. They are found in four areas of the plant cell: the cytoplasm, the surface of the endoplasmic reticulum, the mitochondria, and on chloroplasts. There are two main types of ribosomes: free ribosomes and attached ribosomes. Attached ribosomes are attached to the endoplasmic reticulum and serve as sites for protein synthesis. Proteins synthesized on these ribosomes will be exported from the cell, moved into other organelles of the endomembrane system, or incorporated into membranes. Protein synthesis also occurs on free ribosomes.
So, the correct answer is 'Ribosome'.