Final answer:
The correct answer is A. x = -7, since it represents a vertical line that is perpendicular to the y-axis, which has the general form x = a.
Step-by-step explanation:
The question asks which equation represents a line that is perpendicular to the y-axis. Perpendicular lines to the y-axis are vertical lines, and their equations are given in the form x = a, where a is any real number. This is because vertical lines have an undefined slope and only cross the x-axis at one point, thus they cannot be written in the slope-intercept form y = mx + b.
The correct answer is A. x = -7, as it represents a vertical line that crosses the x-axis at -7 and is perpendicular to the y-axis. None of the other options, B. y = x + 4, C. x = -y, or D. y = 1, represent a line perpendicular to the y-axis since they are not in the form x = a.