The correct answer is:
c. parallel lines have the same slope
Parallel lines never intersect and therefore have identical slopes, which means they will continue to be the same distance apart without converging or diverging. The other options are incorrect because:
- a. Parallel lines do not necessarily have a slope of zero; they can have any constant slope.
- b. Not all parallel lines have undefined slopes; for instance, two non-vertical lines can be parallel with a defined slope.
- d. Negative reciprocals are a relationship that exists between perpendicular lines, not parallel lines.