The correct option is A Altruism
'Regard for others as a principle of action' is Option D, Altruism. Option A, 'Cynicism' is a belief that people are interested only in themselves and are not sincere. Option B 'Nepotism' is. the act of using one's power or influence to get job or advantage for their members of the family. Option C, 'Philanthropy' is the activity of helping poor, especially by giving them money. Thus, options A, B and C are incorrect and the correct word for the phrase is Option D, Altruism.