The graph of the function $y = 22 f(x)$ can be obtained from the graph of $y = f(x)$ by one of the following actions:
(a) horizontally stretching the graph of $f(x)$ by a factor 22;
(b) horizontally shrinking the graph of $f(x)$ by a factor 22;
(c) vertically stretching the graph of $f(x)$ by a factor 22;
(d) vertically shrinking the graph of $f(x)$ by a factor 22;
Your answer is (input a, b, c, or d)