Final answer:
The slope of HI is 0, as it's a horizontal line.
Step-by-step explanation:
The slope of a straight line represents the ratio of the vertical change (rise) to the horizontal change (run) between any two points on the line. The slope can be positive, negative, zero, or undefined.
A horizontal line, such as HI, has a slope of 0 because the vertical change between any two points on the line is zero.
Therefore, the correct answer is A. The slope of HI is 0, as it's a horizontal line.