Final answer:
Transfer RNAs (tRNAs) have extensive secondary structure similar to what the question describes. They are synthesized by RNA polymerase III and intricately fold to facilitate protein synthesis by carrying amino acids and pairing with mRNA codons.
Step-by-step explanation:
The RNA molecules with extensive secondary structure, reminiscent of tRNAs, are Transfer RNAs or tRNAs (Option B). Transfer RNAs are transcribed by RNA polymerase III and fold into a three-dimensional structure through local regions of base pairing stabilized by intramolecular hydrogen bonding. Mature tRNAs feature a complex cloverleaf structure that allows them to carry specific amino acids and recognize the mRNA codons during protein synthesis. The anticodon region of tRNA pairs with the complementary codon on mRNA to ensure the correct incorporation of amino acids into the growing polypeptide chain, which is essential to the process of translation.