[quote="Bunuel"]Birds'
feathers, epidermal outgrowths consisting of shafts and veins interlaced with tiny barbs, serve various purposes; some aiding in flight, others insulating their bodies, and still others offering bright displays for mating rituals.
(A) feathers, epidermal outgrowths consisting of shafts and veins interlaced with tiny barbs, serve various purposes; some aiding in flight, others insulating their bodies, and still others offering
After semi-colon, clause is required(B) feathers are epidermal outgrowths consisting of shafts and veins interlaced with tiny barbs; serving various purposes, aiding in flight, insulating the birds' bodies, and still offering
Same as A(C) feathers, which are epidermal outgrowths consisting of shafts and veins, and serve various purposes: some aid the birds in flight, others insulate the birds' bodies, and still offer
'and' separates the verb 'serve' from its subject 'feathers' (D) feathers are epidermal outgrowths consisting of shafts and veins interlaced with tiny barbs; serving various purposes, with some aiding in flight, others insulate their bodies, with others still offering
Same as A with semi-colon. Moreover, list is not parallel(E) feathers, epidermal outgrowths consisting of shafts and veins interlaced with tiny barbs, serve various purposes: some aid in flight, others insulate the birds' bodies, and still others offer
Seems OKIMO E