Final answer:
Abby holds a dance-off competition to decide who will perform at Nationals in season 2, episode 25 of Dance Moms.
Step-by-step explanation:
In season 2, episode 25, to make a decision about who will perform in Nationals, Abby opts to hold a dance-off competition. This method is often used in the show as a way for her to determine who is the most prepared and deserving to represent the team at the competition.
Abby's decisions and methods for selecting team members are a recurring theme throughout the Dance Moms series, which is known for its intense competitions and the drama surrounding Abby's teaching style and decision-making process.