Answer: The correct answer is -
A) ribosomes.
Ribosomes can be described as subcellular structures that are present within the cells of all living organsisms. They are considered as the site for synthesis of protein from mRNA (messenger RNA), a process that is known as translation.
mRNA strand carries information for protein synthesis in the form of codon (a sequence of three nucleotides that code for particular amino acid). It arrives at ribosome where tRNA molecule brings specific amino acid according to the codon.
The amino acids are assembled in a particular sequence, producing specific protein at this site (that is ribosome).
Thus, the letter 'D' asked in the question corresponds to Ribosomes.