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 an injective homomorphism from V1 to V2

B.f is a surjective homomorphism from V1 to V2

C.f is an isomorphism from V1 to V2

D.none of the above

A．f is an injective homomorphism from V1 to V2

B．f is a surjective homomorphism from V1 to V2

C．f is an isomorphism from V1 to V2

D．none of the above

A.V2＞V3＞V1

B.V1＞V3＞V2

C.V1=V2=V3

D.V2＞V1＞V3

A.V1=6V，V2=4V

B.V1=6V，V2=6V

C.V1=8V，V2=4V

D.V1=8V，V2=6V

A.V1 - V2

B.V2 - V1

C.V1 + V2

D.V1 × V2

A.V1

B.V2

C.V1和V2

D.V1或V2

A.V1≥V2

B.V1≤V2

C.V1=V2

将三相对称负载连接成三角形，如下图所示，图中电压表V₁与V₂的读数为（）

A. ['A、V₁=V₂=220V

B. V₁=V₂=380V

C. V₁=V₂

D. V₂=V₁