What product is used to clean smudged keys on a keyboard?

Answer: Option C

Denatured alcohol is commonly used to clean smudged keys on a keyboard.
It is effective in removing oils, dirt, and grime from keyboard keys without damaging the plastic or rubber components.
TMC solvent and silicone spray are not typically used for cleaning keyboard keys.
An all-purpose cleaner may be too harsh for delicate electronic components and is not recommended for cleaning keyboards.
Therefore, the correct option is denatured alcohol.