This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
R-RNA is mainly produced in 
Select and explain. 
A. Nucleus, B. Nucleolus, C. Ribosome, D. Endoplasmic reticulum
B: Nucleolus
Answer: B: Nucleolus 
Explanation: rRNA is produced by the cell's nucleolus. Ribosomal proteins are translated from mRNA outside the nucleus by ribosomes and then sent back in so they can be used for ribosome subunits assembly in the nucleolus.