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