Suppose f(x)=x^(2) and g(x)=(3x)^(2). Which statement best compares the graph of g(x) with the graph of f(x) ?
A. The graph of g(x) is horizontally compressed by a factor of 3 .
B. The graph of g(x) is shifted 3 units to the right.
C. The graph of g(x) is vertically stretched by a factor of 3 .
D. The graph of g(x) is horizontally stretched by a factor of 3 .