The correct answer is C. strings
Step-by-step explanation:
Personification is a literary device characterized by depicting non-human entities such as animals, objects, among others as humans or as having certain human traits. In the case of "his daughter watched him intensely, and lovingly, as his fingers made the strings sing a song" personification occurs in "the strings sing a song" because although singing is an activity that is related to humans, the author depicts the string as able to sing wich means the author gives an object human characteristics. Thus, the object or concept personified is the strings.