Methylmagnesium bromide, $\mathrm{CH}{}_3\mathrm{MgBr}$, behaves as a source of $\mathrm{CH}{}_3{}^{-}$. With which of the following does it release methane?

The strongly basic carbanion-like carbon takes a proton from any acid stronger than methane. Ethanol (O-H) and propyne (terminal sp C-H) both have such protons. Diethyl ether has only sp3 C-H bonds, and but-2-yne has no acidic sp C-H, so neither liberates methane.