In a referendum, what does a double majority require regarding voters across Australia?

In a referendum, what does a double majority require regarding voters across Australia?

• AA majority of voters across the nation must vote for the change.Correct
• BOnly voters in one state must vote for the change.
• CThe Governor-General must approve the change without a vote.
• DAll voters across the nation must vote for the change.

The fact states that a double majority requires a majority of voters across the nation to vote for the change.