The answer is c) nucleolus.
The nucleolus is a specialized structure within the nucleus of eukaryotic cells where ribosomal RNA (rRNA) is synthesized and combined with proteins to form ribosomal subunits. While other types of RNA, such as messenger RNA (mRNA) and transfer RNA (tRNA), are synthesized in the nucleus, the nucleolus is specifically responsible for the production and initial processing of rRNA. This rRNA is essential for the formation of ribosomes, which are crucial for protein synthesis in the cell. Therefore, the nucleolus plays a critical role in the overall function of eukaryotic cells by contributing to the assembly of ribosomal components.