In which of the following conversions does a carbocation change into a more stable carbocation by a single 1,2-shift?

1. A$(\mathrm{CH}{}_3){}_2\mathrm{C}{}^{+}-\mathrm{CH}{}_2\mathrm{CH}{}_3\to (\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CH}{}^{+}-\mathrm{CH}{}_3$ (hydride shift)
2. B$(\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CH}{}_2{}^{+}\to (\mathrm{CH}{}_3){}_3\mathrm{C}{}^{+}$ (hydride shift)
3. C$(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{CH}{}_2{}^{+}\to (\mathrm{CH}{}_3){}_2\mathrm{C}{}^{+}-\mathrm{CH}{}_2\mathrm{CH}{}_3$ (methyl shift)
4. D$(\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CH}{}^{+}-\mathrm{CH}{}_3\to (\mathrm{CH}{}_3){}_2\mathrm{C}{}^{+}-\mathrm{CH}{}_2\mathrm{CH}{}_3$ (hydride shift)