The correct option is
B Wistful
'Nostalgic' means feeling happy and also slightly sad when you think about things that happened in the past.
Option A - 'Indolent' means showing no real interest or effort. Thus option A is incorrect.
Option B - 'Diseased' means someone who is suffering from a disease. Thus option B is incorrect.
Option D - 'Soothing' means someone or something that makes you feel calm. Thus option D is incorrect.
Option C - 'Wistful' means sad or thinking about something that is impossible or that was in the past. Thus option C is the correct answer.
'Nostalgic - Wistful'