c) detecting {HEAD ~ light} of such wavelength that is reflected or scattered by {TAIL ~ the sheet}, and 
c ) detecting { HEAD ~ light } of such wavelength that is reflected or scattered by { TAIL ~ the sheet } , and
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH