Why do vaccine makers have to guess which flu strains will be active months before the flu season begins?

Read the sentence from susan b. anthony's "on women's right to vote." hence, every discrimination against women in the constitutions and laws of the several states is today null and void, precisely as is every one against negroes. in this sentence, the author's tone is best described as

Accepted is to fact as unproven is to

Based on this excerpt the authors are most likely to attempt to answer which question