How long should you stop behind a school bus with flashing red lights?

• Until you no longer see students boarding or exiting
• For as long as you choose
• Until the flashing red lights turn off and the stop sign is retracted
  Explanation:

  "You must remain stopped behind a school bus until the alternating flashing red lights are turned off and the stop sign on the driver’s side is no longer extended. "
• All of the above