Answer:
C
Step-by-step explanation:
The slope of a horizontal line, such as that of y= 3, is equal to 0.
This can be proved using the slope formula.
[tex]\boxed{ slope = \frac{y _{1} - y_2 }{x_1 - x_2} }[/tex]
Let's choose 2 points on the line y= 3:
(0, 3) and (2, 3)
Slope
[tex] = \frac{3 - 3}{2 - 0} [/tex]
[tex] = \frac{0}{2} [/tex]
= 0
Thus, the line has a slope of zero.
On the other hand, vertical lines have an undefined slope.
Additional:
To learn more about horizontal lines and their slopes, do check out the following!