We can see the difference between the red and black graphs is that the red graph is one unit higher in the y direction. Since there are no other differences, it is not possible to change to the input of the equation and achieve the red graph. Therefore answers a and b are not possible. If D was the answer, the red graph would be mirrored across the x axis. Answer c can be rearranged to y=f(x)+1 which would increase f(x) by 1.
