When the Supreme Court Announced the Principle of "One Person,one

When the Supreme Court announced the principle of "one person,one vote," what did it mean?

A) Voters may only vote once in an election.
B) Within a state,electoral districts must have roughly equal populations.
C) No one could be denied suffrage on the basis of race or gender.
D) Voting was an individual right,not a group right.
E) Compulsory voting is constitutional.