Which of the following carbocations are stabilised by resonance (delocalisation involving a pi bond or lone pair)?

In $\mathrm{CH}{}_3\mathrm{OCH}{}_2{}^{+}$ the oxygen lone pair overlaps with the empty p orbital, and in the benzyl cation the ring pi system does. The tert-butyl cation is stabilised only by hyperconjugation and +I. In $\mathrm{CH}{}_2=\mathrm{CH}-\mathrm{CH}{}_2-\mathrm{CH}{}_2{}^{+}$ an sp3 carbon separates the pi bond from the cationic centre, so there is no conjugation.