One reflector in each module is concave, and {HEAD ~ the modules} are asymmetric in {TAIL ~ section}, although two asymmetric modules may be combined in a system which is itself symmetrical 
are asymmetric in
One reflector in each module is concave , and { HEAD ~ the modules } are asymmetric in { TAIL ~ section } , although two asymmetric modules may be combined in a system which is itself symmetrical
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH