In which of the following compounds is resonance of a substituent with the ring significantly diminished by steric inhibition of resonance?

In the first three compounds, two groups flank the conjugating substituent and force it out of the ring plane: $-\mathrm{N}(\mathrm{CH}{}_3){}_2$, $-\mathrm{NO}{}_2$ and $-\mathrm{COOH}$ respectively, so their orbital overlap with the ring is lost. In 4-nitrophenol the nitro group is unhindered and coplanar.