"Ribosomes are described as the site of protein synthesis. Ribosomes consist of RNA and protein combined into a very particular shape. As a ribosome moves along an mRNA transcript, amino acids are joined together by peptide bonds. The formation of peptide bonds is facilitated by rRNA in the ribosome. Thus, rRNA can be described as a(n)"

Catalyst

Explanation:

Translation is the second process of gene expression which occurs in the ribosomes of living cells. The ribosome is a complex of Ribosomal RNA (rRNA) and proteins. Translation occurs when ribosomes attach to the transcribed mRNA molecule to read its codons using the transfer RNA (tRNA's) anticodon. The tRNA then carries amino acid that corresponds the codon it reads to the growing polypeptide chain.

In this process, amino acids are attached to one another forming a peptide bond. This linking of one amino acid to another is facilitated by rRNA's as it helps catalyzes the reaction like an enzyme. Ribosomal RNA catalyzes the reaction that forms a peptide bond between the amino acid in the A site of the ribosome and the growing polypeptide (future protein) in the P site.

i believe the correct answer is d