how many points on the graph represent a relative minimum? please help

Point B is the only relative minimum here.
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Explanation:
A relative minimum is a valley point, or lowest point, in a given neighborhood. Points to the left and right of the valley point must be larger than the relative min (or else you'd have some other lower point to negate its relative min-ness).
Point B is the only point that fits the description mentioned in the first paragraph. For a certain neighborhood, B is the lowest valley point so that's why we have a relative min here.
There's only 1 such valley point in this graph.
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Side notes: