Your web application needs four instances to support steady traffic all of the time. On the last day of the month, the traffic triples. What is the most cost$-$effective way to handle this pattern? $($Select the best answer$)$

Answer options:

Run $12$ Reserved Instances all of the time.

Run four On$-$Demand Instances constantly, then add eight more On$-$Demand Instances on the last day of each month.

Run four Reserved Instances constantly, then add eight On$-$Demand Instances on the last day of each month.

Run four On$-$Demand Instances constantly, then add eight Reserved Instances on the last day of each month.