$(4,8)$ and $(4,-9)$ Select the correct choice below and fill in the answer box within your choice. A. The slope is $\square$. (Simplify your answer.) B. The slope is undefined. Indicate whether the line through the points rises, falls, is horizontal, or is vertical. The line rises from left to right. The line is vertical. The line falls from left to right. The line is horizontal.

Step 1 ：Given two points (4,8) and (4,-9).

Step 2 ：The slope of a line passing through two points (x1, y1) and (x2, y2) is given by the formula \(\frac{y2 - y1}{x2 - x1}\).

Step 3 ：Substitute the given points into the formula to get \(\frac{-9 - 8}{4 - 4}\).

Step 4 ：The denominator is zero, which means the slope is undefined.

Step 5 ：This happens when the line is vertical.

Step 6 ：\(\boxed{\text{The slope is undefined. The line is vertical.}}\)