Answer:
The correct answer is: the sense of duty toward one's family.
Step-by-step explanation:
You can see in the line: “felt a great pride that he was able to provide a life like that in such a nice home for his sister and parents” that Gregor feels responsible for providing that in some way to his family, as well as in the line: “if all this peace and wealth and comfort should come to a horrible and frightening end? That was something that Gregor did not want to think about too much”, he also feels responsible if something bad would happen. In other words, -a sense of duty- means to feel morally obligated towards someone or something, it can be in a good way; feeling happy for the achievements or sad for not being able to do it properly, or in a bad way; always complaining and doing it only because you have no other choice.