The structure of biphenyl and the numbering scheme used in naming its derivatives are indicated below. What is the major product obtained on dinitration of biphenyl (HNO3, H2SO4)?
a. 2,4-Dinitrobiphenyl
b. 2,6-Dinitrobiphenyl
c. 3,5-Dinitrobiphenyl
d. 3,3'-Dinitrobiphenyl
e. 4,4'-Dinitrobiphenyl