Question

in order to vote, what must a person do prior to election day?
obtain a seal on their registration card
register with the board of elections
be over 21 years of age

Explanation:

To vote, a key requirement before Election Day is voter registration. "Obtain a seal on their registration card" is not a standard pre - election requirement. Also, the voting age in many places (like the US) is 18, not 21, so "be over 21 years of age" is incorrect. Registering with the board of elections is the correct pre - Election Day action for voting eligibility.

Answer:

B. register with the board of elections