Explanation
The nucleolus takes part in the synthesis of ribosomal RNA (rRNA).
The nucleolus is a specialized structure within the nucleus of eukaryotic cells that is responsible for producing the subunits of ribosomes. Ribosomes are the cellular machinery responsible for protein synthesis, and they are composed of two subunits, each of which is made up of rRNA and proteins. The nucleolus is the site where rRNA is transcribed from DNA and assembled with proteins to form the ribosomal subunits.
Therefore, option A (rRNA) is the correct answer.
Option B (tRNA) is incorrect because tRNA is synthesized in the nucleus but outside the nucleolus.
Option C (mRNA) is incorrect because mRNA is synthesized in the nucleus but outside the nucleolus, and it is involved in protein synthesis in the cytoplasm.
Option D (DNA) is incorrect because the nucleolus is not directly involved in DNA synthesis.
