{HEAD ~ The first scan unit} 110 comprises an exposure lamp 114 and {TAIL ~ a first reflection mirror} 115 
comprises
{ HEAD ~ The first scan unit } 110 comprises an exposure lamp 114 and { TAIL ~ a first reflection mirror } 115
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH