The correct answer is A. Methyl alcohol.
Methyl alcohol, also known as wood alcohol, is a colorless, flammable liquid that is used as a solvent and fuel. It is also used to denature ethanol, which is the process of adding a poisonous substance to ethanol to make it unfit for human consumption.
Propyl alcohol, also known as isopropyl alcohol, is a colorless, flammable liquid that is used as a solvent and antiseptic. It is not used to denature ethanol.
Phenol, also known as carbolic acid, is a white, crystalline solid that is used as a disinfectant and antiseptic. It is not used to denature ethanol.
Methane is a colorless, odorless, flammable gas that is the main component of natural gas. It is not used to denature ethanol.