O–S–S–O has three resonance Lewis structures that complete the octet for all the atoms. Which statements about these structures are correct?

I. All are equivalent.

 II. All are nonequivalent.

 III. Two are equivalent, and one is nonequivalent. 

IV. The formal charges on all the atoms are zero in at least one structure. 

V. All the bonds have double-bond character. 

a. II and IV         

 b. I and IV 

 c. III and V

d. I and V

e. III, IV, and V