If f(x) = x^2, 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) = x^2 one unit to the left.
B.) The graph of f(x - 1) is a vertical shift of f(x) = x^2 one unit up.
C.) The graph of f(x - 1) is a horizontal shift of f(x) = x^2 one unit to the right.
D.) The graph of f(x - 1) is a vertical shift of f(x) = x^2 one unit down.