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Call walked the river for an hour, though he knew there was no real need. It was just an old habit he had, left over from wilder times: checking, looking for [a] sign of one kind or another, honing his instincts, as much as anything. In his years as a Ranger captain it had been his habit to get off by himself for a time, every night, out of camp and away from whatever talking and bickering were going on.
As used in the passage, the word “honing” (line 4)
most nearly means
(A) forgetting (C) measuring
(B) ignoring (D) sharpening
What is D. sharpening