Benzene is C6H6; here's the Lewis structure with resonance
(b) Are the C-C bond lengths in benzene shorter than C-C single bonds? Are they shorter than C=C double bonds?
Look at the Lewis structures above: since we can draw more than one acceptable structure by moving double bonds, we have resonance. We think of the carbon-carbon bonds as sort of a 'blend' of the two resonance structures - all the C-C bond lengths are intermediate in length between a C-C single bond and a C=C double bond (the actual bond lengths in benzene are shorter than a pure C-C single bond but longer than a C=C double bond.