The correct option is A A character describes his dislike for his new job and considers the reasons why.
Option A: This is the most suitable option. The passage begins with "No man likes to acknowledge that he has made a mistake in the choice of his profession".
The narrator goes on to admit that his job is 'irksome': "I felt my occupation irksome." and reflects on the reasons for his dislike. He says that his work is a "dry and tedious task" and that he has a bad rapport with his superior: "the antipathy which had sprung up between myself and my employer striking deeper root and spreading denser shade daily excluded me from every glimpse of the sunshine of life; and I began to feel like a plant growing in humid darkness out of the slimy walls of a well."
Hence option A is correct.
Option B: The narrator does not become increasingly competitive with his superior. On the other hand, his superior feels insecure around him as he is as good as him.
Option C: It is neither mentioned nor implied that in the passage that the narrator publicly defends his choice.
Option D: The narrator does not begin the passage with any optimism about his job.
Hence options B, C and D are incorrect.