Final answer:
The monster's act of saving a girl from drowning showcases his good side the most, reflecting his kindness and bravery.
Step-by-step explanation:
The event that best illustrates the monster's good side in Mary Shelley's Frankenstein is C) Saving a girl who is about to drown. This action demonstrates the creature's capacity for compassion and heroism, despite being shunned and misunderstood by society. The monster's act of saving the girl shows that he possesses a humane and empathetic nature, which contrasts with the horror and fear that his appearance often elicits. Choice B) Watching the family in the cottage in order to learn human interaction does show his desire to understand and connect with humans but does not as clearly illustrate his innate goodness. Meanwhile, choice D) Leaving gold pieces on the doorstep of the family's cottage is a kind gesture but does not necessarily demonstrate the selflessness and bravery implicit in saving a person's life. Lastly, A) Running from Frankenstein after being created is more a reaction to his circumstances than a deliberate act of kindness or goodness.