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