National Film Award for Best Film on Environment Conservation/Preservation
It was not presented on nine occasion in 1990 ( 38th ceremony ) , 1991 ( 39th ceremony ) , 1996 ( 44th ceremony ) , 2001 ( 49th ceremony ) , 2002 ( 50th ceremony ) , 2006 ( 54th ceremony ) , 2007 ( 55th ceremony ) , 2009 ( 57th ceremony ) , and 2011 ( 59th ceremony ) . 
<triplet> 1990 (38th ceremony) <subj> 1991 (39th ceremony) <obj> followed by <subj> 1991 <obj> point in time <triplet> 2001 (49th ceremony) <subj> 2002 (50th ceremony) <obj> followed by