Answer: Undefined.
- A 0
- B 1
- C Undefined
- D -1
Correct answer: C. Undefined
Explanation: A vertical line has undefined slope (infinite rise, zero run).
The slope of a line is the ratio of vertical change (rise) to horizontal change (run) between any two points on it - equivalently, the tangent of the angle θ the line makes with the positive x-axis.