Which pair is correctly labelled with its type of isomerism?

Diethyl ether and methyl propyl ether are ethers with different alkyl groups on oxygen: metamers. Butan-1-ol and tert-butyl alcohol differ in carbon skeleton (chain isomerism), propanal and propanone are functional isomers, and nitroethane ($\mathrm{C}{}_2\mathrm{H}{}_5\mathrm{NO}{}_2$) and propanenitrile ($\mathrm{C}{}_3\mathrm{H}{}_5\mathrm{N}$) are not even isomers.