This question tests the understanding of metaphors in the text. The correct answer is B because 'covering my exit' is used metaphorically to mean that the author is掩饰ing the real reason for leaving her job. Option A is incorrect because it takes the phrase literally, which is not the case in the passage. Option C is wrong because there is no mention of a physical barrier. Option D is incorrect because it misinterprets the metaphor as referring to the difficulty of leaving employment in general, rather than hiding the reason.