Often on a topographic map, every fifth contour line is darkened. what is thisline called? оа) keyob) slopeoc) benchmarkod) index countour

that would be called plucking : )

explanation:

''plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". as a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock."

the answer you are looking for is the united states forest service.

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radon is correct hope this