I would imagine it would be C. But I am only writing this to sway you if you were already considering C as the most likely answer. Do not take this as a completely true or correct answer to the question.
Since the climax is when the turning point of the story happens and makes a choice to solve the conflict I think that it is B The detective looks for clues about who the thief might be! Sorry if I am wrong but I am confident this is the answer.