For which of the following functions is f(a+b) = f(a) + f(b) for all positive numbers a and b?
f(x) = x^2
f(x) = x+1
f(x) = root(x)
f(x) = 2/root(x)
f(x) = -3x
OA: E
f(x) = x^2
f(x) = x+1
f(x) = root(x)
f(x) = 2/root(x)
f(x) = -3x
OA: E
