You are approaching a swing bridge at night. You will know that the bridge is open for river traffic when __________.

Correct Answer: Option B — the red light changes to green

In USCG General Navigation principles (Bowditch, Light Lists, and Coast Pilots), regarding 'You are approaching a swing bridge at night. You will know that the bridge is open for river traffic when', the verified fact is: 'the red light changes to green'.