Given the statement "If a line is horizontal, then it has slope equal to zero,” what is its contrapositive?

For a conditional statement “if P, then Q,” its contrapositive is “if not Q, then not P.” Here, P is “the line is horizontal” and Q is “the line has slope equal to zero.” So the contrapositive is “If a line does not have zero slope, then it is not a horizontal line,” which is choice D.

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