Protein synthesis in a bacterial cell is done by

The correct answer is D. Ribosomes.

Ribosomes are the organelles in the cell that are responsible for protein synthesis. They are made up of two subunits, a large subunit and a small subunit. The large subunit contains the active site where the protein is synthesized, while the small subunit helps to bring the amino acids together in the correct order.

Centrioles are small organelles that are found in animal cells. They are involved in cell division.

Flagella are long, whip-like structures that are found on some bacteria. They are used for locomotion.

Thylakoids are membrane-bound sacs that are found in chloroplasts. They are involved in photosynthesis.