When are pedestrians required to stop at a railroad-highway grade crossing?

• When a human flagger is giving warning of an approaching train
• When an approaching train is clearly visible
• When warning devices are flashing
• All of the above
  Explanation:

  "Pedestrians are required to stop upon approaching a railroad-highway grade crossing when: 1. When a human flagger is warning of an approaching train. 2. When an approaching train is clearly visible. 3. When warning devices are flashing."