Which of the following on treatment with warm dilute $H_2SO_4$ in the presence of $HgSO_4$ will give butan-2-one?

$\begin{array}{1 1}(a)\;\text{But-1-yne,But-2-yne}&(b)\;\text{But-3-yne}\\(c)\;\text{But-1-ene}&(d)\;\text{But-2-ene}\end{array}$