The correct option is A a - 4, b - 2, c - 3, d - 1
Messenger RNAs (mRNAs) specify the amino acid sequence of one or more polypeptides; a set of three nucleotides forms a codon which in turn specifies a particular amino acid. Thus, it transfers genetic information from DNA to ribosomes. Transfer RNAs (tRNAs) read the genetic information present in the form of triplets in the mRNA and transfer the appropriate amino acid to a growing polypeptide chain during protein synthesis. The darkly stained body in the nucleus is nucleolus which is involved in ribosome construction. It makes around a nucleolar organizer region on one of the chromosome pairs. The peptidyl transferase forms peptide bond between the carboxyl group of peptidyl tRNA present at P site and a free amino group of peptidyl tRNA present at A site.