If f(x) = x2, which of the following describes the graph of f(x - 1)? A. The graph of f(x - 1) is a horizontal shift of f(x) = x2 one unit to the right. B. The graph of f(x - 1) is a vertical shift of f(x) = x2 one unit down. C. The graph of f(x - 1) is a vertical shift of f(x) = x2 one unit up. D. The graph of f(x - 1) is a horizontal shift of f(x) = x2 one unit to the left.