Concept:The given expression means succeeding by the smallest possible difference, or just barely managing to do something.Explanation:Phrases like "by the skin of one's teeth" or "by a hair's breadth" are used when a person passes, wins, or survives only just in time.This shows that the result was very close and could have easily gone the other way.It does not mean default, lack of preparation, or success by a wide gap.Thus, the most suitable interpretation is success with only a small difference between success and failure.Answer:D. a narrow margin