Answer:
x- axis
Explanation:
We are given that any line whose slope is zero.
We have to find the line with a slope of zero is parallel to which axis.
We know that when any line is parallel to x- axis
It means y does not change with
Therefore,

Slope of a line which is parallel to x- axis is zero because y does not vary with x.
But when a line parallel to y - axis then slope of that line is undefined.
When line y=x
Then ,

Hence, any line with slope of zero is parallel to the x- axis.
Answer:x- axis.