Which of the following compounds reacts with sodamide ($\mathrm{NaNH}{}_2$) to give a sodium salt with evolution of ammonia?

Only a terminal alkyne has an sp-hybridised C-H bond acidic enough (pKa about 25) to be deprotonated by the amide ion (conjugate acid ammonia, pKa 38). But-1-yne gives sodium but-1-yn-1-ide; but-2-yne has no sp C-H, and the alkene and alkane C-H bonds are much less acidic.