In which of the following pairs do the two alcohols give the same major alkene on dehydration with conc. $\mathrm{H}{}_2\mathrm{SO}{}_4$ at about 440 K?

2-Methylpropan-1-ol (via hydride shift) and 2-methylpropan-2-ol both give 2-methylpropene, and the two propanols both give propene. Pentan-3-ol gives pent-2-ene and pentan-2-ol also gives mainly pent-2-ene by the Saytzeff rule. Butan-2-ol gives but-2-ene, but 2-methylpropan-2-ol gives 2-methylpropene.