Choice C is the best answer. The first paragraph shifts from a general discussion of how people deal with choosing an occupation they later regret (lines 1-6,"No...land") to the narrator's description of his own dissatisfaction with his occupation (lines 6-33,"From...well").
Choices A, B, and D are incorrect because the first paragraph does not focus on the narrator's self-doubt, his expectations of life as a tradesman, or his identification of alternatives to his current occupation.