The correct response to explain why the slope is the same between any two distinct points on a nonvertical line is:
"The legs of similar triangles used at different points along the line represent the rise and run of the line, or its slope. The corresponding sides of similar triangles are proportional, so the slope can be shown as the same using any two points along the line."
This response accurately describes how similar triangles formed from the line have proportional sides, leading to a consistent slope between any two points on the line.