Using pairs of opposites, such as Helena and Hermia, is called

A. doubling.

B. foreshadowing.

C. irony.

D. realism.

A. doubling

In literature, doubling creates contrast by juxtaposing two opposite character, similar to the idea of "two sides of the same coin". Therefore choice A is the correct answer. Two characters on their own do not necessarily show realism or irony and it is the plot and dialogue that would display foreshadowing. So choice B, C and D are incorrect.