Ribosomes are the cell parts that MAKE or synthesize proteins. In Eukaryotic cells, some ribosomes are floating free in the cytoplasm and make the proteins there. Sometimes, the ribosomes may land on the Rough Endoplasmic Reticulum and make the proteins there (sticking the proteins as they're made into the RER where the proteins can be modified, etc). That's a long way to say you should be careful answering that question. The teacher may be asking "what cell part synthesizes proteins" OR "where in the cell does that synthesis occur?" I'd take the safe way out and say "ribosomes can synthesize proteins either on the Rough Endoplasmic Reticulum or while floating around in the cytoplasm" That way, you're fully answering the question and including enough information that whatever "right" answer the teacher is looking for is in your answer.