Geometry

Question Analysis
This question tests the understanding of the relationship between the slopes of perpendicular lines. Specifically, it assesses the knowledge that a line perpendicular to a horizontal line (slope = 0) must be vertical (undefined slope).

Key Concept Explanation
The slope of a horizontal line is 0. For two lines to be perpendicular, the product of their slopes must be -1. Since the slope of a horizontal line is 0, the only way to satisfy this condition is for the other line to be vertical, which has an undefined slope.

Step-by-step Solution
1. Identify the slope of the given line: The slope of a horizontal line is 0.
2. Determine the condition for perpendicularity: For two lines to be perpendicular, the product of their slopes must be -1.
3. Apply the condition: If one line has a slope of 0, the other line must have an undefined slope to satisfy the condition , where

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