In order to meet a state’s residency requirement for voting, people must prove they
a. have already registered to vote
b. have lived in a state for a certain amount of time
c. are over the age of 21
d. will soon be a united states citizen

In order to meet a state’s residency requirement for voting, people must prove they b. have lived in a state for a certain amount of time. A residency requirement is one of the guidelines in voting. Residency is defined as a location where a person has lived in with an intent to stay or return. People can only have 1 legal residence at a time.

It's most likely choice a, it makes the most sense in my opinion.