The vertical transformation of a linear function of the form
[tex]y=mx+b[/tex]
is the shift of the y-intercept b; meaning, the vertical transformation only changes the value of b and leaves the slope unchanged.
Hence, the vertical transformation of functions leaves the slope unchanged, meaning choice A is correct one
Just to make sure we have got the right answer let us probe other answer choices.
Choice B is not correct since it implies that parallel lines should meet.
Choice C is not correct since the value of b is changed in the transformation, and therefore, the original equation and the transformed equation are not the same.
The function y = b is also a linear function but with slope zero and changing b here also counts as a vertical transformation - so this choice D is wrong.