Final answer:
mRNA is excluded as a noncoding RNA because it carries the genetic code from DNA for protein synthesis, unlike rRNA, tRNA, and regulatory RNAs like miRNA that play other roles in the cell.
Step-by-step explanation:
Noncoding RNAs include all of the following EXCEPT C. mRNA. This is because messenger RNA (mRNA) is indeed involved in coding, as it carries the genetic information from DNA to the ribosome, where proteins are synthesized. In contrast, rRNA (ribosomal RNA), tRNA (transfer RNA), and regulatory RNAs such as miRNA (microRNA) and long non-coding RNAs (lncRNAs), do not code for proteins but perform various other roles in the cell.
For example, rRNA is a structural component of ribosomes and plays a role in protein synthesis; tRNA is responsible for bringing amino acids to the growing peptide chain during translation; and miRNA regulates gene expression by interfering with mRNA activity.