Which statement is true about the graphs of the two lines y = –6 and x = ?

a. the lines are perpendicular to each other because the graph of y = –6 is a horizontal line with a slope that is undefined, and the graph of x = is a vertical line with a slope of 0.
b. the lines are perpendicular to each other because the graph of y = –6 is a vertical line with a slope that is undefined, and the graph of x = is a horizontal line with a slope of 0.
c. the lines are perpendicular to each other because the graph of y = –6 is a vertical line with a slope of 0, and the graph of x = is a horizontal line with a slope that is undefined.
d. the lines are perpendicular to each other because the graph of y = –6 is a horizontal line with a slope of 0, and the graph of x = is a vertical line with a slope that is undefined.