A pair of parallelly disposed vertical trollies are attached to the side of the building on {HEAD ~ opposite sides} of {TAIL ~ a plurality} of emergency exits 
of
A pair of parallelly disposed vertical trollies are attached to the side of the building on { HEAD ~ opposite sides } of { TAIL ~ a plurality } of emergency exits
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH