The protein manufacturing unit in a human cell is the ribosome, making choice (A) the suitable solution. Ribosomes are the cell structures answerable for synthesizing proteins by means of translating messenger RNA (mRNA) into polypeptide chains. They can be located unfastened-floating in the cytoplasm or attached to the endoplasmic reticulum, forming the hard ER. While the nucleus is concerned in DNA replication and transcription, the cytoplasm is the web page where ribosomes perform, and the Golgi apparatus is involved in modifying, sorting, and packaging proteins, the actual synthesis of proteins occurs at the ribosomes.