3) Which of the following is/are group homomorphism(s)?
I- $f: (Z,+) \to (Z,+), f(n) = 2^n$
II- $f: (Z,+) \to (Z,+), f(n) = n^2$
III- $f: (R^+, \cdot) \to (R, +), f(x) = \ln(x)$
a) I only
b) I and III
c) II and III
d) III only
e) I, II and III
f) None