The correct answer is C. Noun
Step-by-step explanation
A noun is a type of word that is used to designate beings, entities, or objects. One of the characteristics of nouns is that they have a masculine or feminine gender and a singular or plural number. According to the above, in the text of the question, the word Courage of the sentence "Ahn thought she would not have the courage to initiate a friendship, but she underestimated herself." is used as a noun because it designates courage as a singular entity. So the correct answer is C. Noun.