A cynic is a person who always finds fault in others, with the belief that human conduct is wholly motivated by self-interest. For example, 'Cynics would question the intentions of the priest who carried out a hunger strike.'
Cynics find faults in others without attempting to find out the truth. Hence the given sentence correctly describes option C, and C is correct.
'Cupid' is the name of the Roman god of love, it has no relation to the given sentence; (playing cupid means 'matchmaking') hence option C is correct.
'Kleptomaniac' refers to a psychological disorder that tempts a person to steal. Hence the sentence does not define this word and option B is incorrect.
'Crone' means 'an ugly woman', it is an insult, whereas the given sentence describes a person in terms of their nature. Hence option D is incorrect.