Generally, if you hear the siren of an emergency vehicle you should:

• A. Pull over to the left until the emergency vehicle passes.
  Explanation:

  "Pulling over to the left will give the emergency vehicle as much space as possible to overtake you. Don't brake heavily or you risk the emergency vehicle running into the back of your vehicle, or another vehicle behind you running into you."
• B. Immediately come to a stop.
• C. Let the emergency vehicle pass and follow it closely behind.