Answer:
The possible theme of The Metamorphosis is A. A lonely and unfulfilling life can make a person very unhappy.
Step-by-step explanation:
Isolation and alienation are two very important elements in this story, as the character of Gregor feels extremely unhappy and unsatisfied with his life, he es immerse in a job that he hates but supports his family and when he gets "rid of it" and afterward his transformation happens he becomes a lonely creator by being unable to communicate with others.