BE CAREFUL. Here we ask about the nucleolus precisely and not about the nucleus in general, the precise role of the nucleolus is to assemble the ribosomal RNA and the ribosomal proteins to form the ribosomes. So the answer is B.
In cell biology, the nucleolus is the largest nucleus subcompartment of eukaryotic cells. This particular space of the nucleus is not delimited by a membrane, nevertheless some authors consider it as an organelle and others do not. The number of nucleoli can vary during the cell cycle (usually only 1 in G0 phase).
The nucleolus is composed of proteins, DNA and RNA and is formed around particular chromosomal regions called NOR (Nucleolar Organizing Regions).
It is in particular the place where the transcription of the ribosomal RNAs (5.8S, 18S and 28S rRNA), the processing of these ribosomal RNAs from precursors and the first part of the assembly of the two ribosome subunits takes place. with the association of certain ribosomal proteins. The end of the ribosome assembly occurs in the cytoplasm on mRNA after export of pre-ribosomes through the nuclear pore.
