Based on the question, it seems safe to assume that we're talking about a parabola in vertex form:
y = a(x-h)² + k, where the vertex is located at point (h, k), and the a value determines the direction (positive or negative) and steepness (absolute value of a) of the parabola.
h is the x value of the vertex. When we change the x value, it will move left or right. I'm not sure why the orders are different (the options go from a to c to b), but the correct is:
It shifts to the left or the right.
