Which of the following carbanions is stabilised by resonance?

A carbanion is resonance stabilised only if its lone pair can be delocalised into an adjacent pi system. In the benzyl anion the lone pair on $\mathrm{CH}{}_2$ overlaps with the ring pi system and the charge is spread to the ortho and para carbons. The ethyl, isopropyl and methyl anions have no pi system, so they are not resonance stabilised.