The answer is probably air.
The material or substance on which an enzyme acts upon is known as the substrate, they are nothing but reacting molecules and or substances that are able to ultimately be converted to product substances. By the aid of biological enzymes, that lower the energy of activation needed for a chemical reaction to proceed.
The RNA codon will be GAU, pairing Cytosine-Thymine-Adenine DNA codon with Guanine-Adenine-Uracil RNA codon. This codon is the Amino Acid, Aspartic Acid. In this codon we see Uracil which is the counterpart of Thymine in the RNA.
The answer is D) proteins