If we kept the red curve completely fixed in place, and only moved the xy axis, then we can move the xy axis 5 units to the right to give the illusion the red curve is moving (even though it's fixed in place).
Moving the xy axis 5 units to the right means each x input is 5 units larger. So x jumps up to x+5
In other words, going from f(x) to f(x+5) will shift the f(x) curve 5 units to the left. So that's why we go from x^2 to (x+5)^2 which is what choice D shows.
