Which of the following liberates methane when treated with excess $\mathrm{CH}{}_3\mathrm{MgBr}$ in dry ether?

Methane forms only when the Grignard reagent finds an acidic proton. The hydroxyl proton of the tertiary alcohol and the terminal alkyne proton ($sp$ C-H) are acidic enough. Dimethyl ether and hexane have no acidic hydrogen and do not react.