The modulated wave has side band frequencies . The AM wave has terms of frequencies , . The wave to be filtered has sinusoids of frequencies , , , , . We need to eliminate , , which do not lie between .Hence, the gain should be maximum between these two values as the AM wave lies between these frequency.

The correct graph is (iii). But we can also get this graph by combining (i) and (ii) in any order. Hence, the correct options are (a), (b) and (c).