Abstract nouns are nouns that cannot be perceived by any of our senses, like sight and smell. They're ideas, concepts and states of being. In the sentence, the italicized words 'wisdom' and 'strength' are both abstract nouns. 'Wisdom' is the state of being wise and 'strength' is the quality of being strong. They're abstract nouns, hence option C is correct. Collective nouns refer to a group of people, animals or objects. the nouns 'wisdom' and 'strength' do not refer to a group, hence option A is incorrect. Concrete nouns are nouns that can be perceived by at least one of our senses, for example, a man is concrete, but his wisdom and strength are abstract, hence option B is incorrect. Option D is incorrect because the nouns are abstract, as in option C.