The correct answer is C. R-RNA.
The nucleolus is a dense, spherical structure found in the nucleus of eukaryotic cells. It is responsible for the synthesis of ribosomal RNA (rRNA), which is a component of ribosomes. Ribosomes are the protein-synthesizing machinery of the cell.
DNA is the genetic material of the cell. It is located in the nucleus and is responsible for storing and transmitting genetic information.
mRNA is a type of RNA that is used to carry the genetic information from DNA to the ribosomes.
tRNA is a type of RNA that is used to translate the genetic information from mRNA into proteins.
In conclusion, the nucleolus is responsible for the synthesis of rRNA, which is a component of ribosomes. Ribosomes are the protein-synthesizing machinery of the cell.