Suppose V1=，V2=，where R is the set of real numbers，+， and are respectively addition and multiplication. Let f: R→R and f(x)=ex，which of the following propositions is true
A．f is a surjective homomorphism from V1 to V2
B．f is an injective homomorphism from V1 to V2
C．f is an isomorphism from V1 to V2
D．None of the above