Answer:
B. to illustrate how unhappy his childhood was
Step-by-step explanation:
THe author adds the argument between his parents in order to show how he lacked certain things in his childhood, and how he wasn´t bery happy with his own childhood, and the situation that he was living in, exemplifying its childhood and how it was unhappy. That helped him give the character motivations and a better understanding of his diverse actions and desires.