Final answer:
Holly and Glen intended to get married soon after their arrival in Las Vegas, making option C the correct answer to what they did next.
Step-by-step explanation:
Based on the context provided, Holly and Glen's next action after hopping on a plane to Vegas is indicated by the phrase: 'They had decided to be married as soon as possible'. This indicates that their intent was to get married once they arrived in Las Vegas. Therefore, the correct answer to what they did next is C. They got married.