When looking at th graph we can discard 2 of the options, these are rotation (as they are parallel, it is impossible to find a rotation axis) and reflection. We can observe that it occur a translation. To know what kind of translation happened, let's look at the y intercept of both lines.
For f(x) the y intercept is 0 and for g(x) the y intercept is -4, it means it occured a vertical translation down 4 units.
The right answer is D.