Let f be a function defined on the set of positive rational numbers with the property that f(a · b) = f(a) + f(b) for all positive rational numbers a and b. Suppose that f also has the property that f(p) = p for every prime number p. For which of the following numbers x is f(x) < 0?
a. 17/32
b. 11/16
c. 7/9
d. 7/6
e. 25/11