The correct answer is:
d. Parallel lines have the same slope.
Explanation:
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a. Parallel lines have slopes that are undefined: This is not true for all parallel lines. It is only true for vertical lines, which are a specific case. However, not all parallel lines are vertical.
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b. Parallel lines have a slope of zero: This statement applies to horizontal lines specifically, but not all parallel lines are horizontal. Therefore, this is also not true for all parallel lines.
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c. Parallel lines have slopes that are negative reciprocals of each other: This is false. Negative reciprocals apply to perpendicular lines, not parallel lines. For example, if one line has a slope of 2, a line perpendicular to it would have a slope of -1/2, while a parallel line would have the same slope of 2.
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d. Parallel lines have the same slope: This statement is true. By definition, parallel lines never intersect and therefore have identical slopes.
Thus, option d accurately describes the relationship between the slopes of parallel lines.