You are approaching a drawbridge and have sounded the proper whistle signal requesting it to open. You hear a signal of one prolonged and one short blast from the bridge. Which action should you take?

Correct Answer: Option B — Approach under full control to pass through the bridge.

Under 33 CFR navigation rules, a drawbridge signal of one prolonged and one short blast indicates that the bridge is opening in response to your request, requiring you to approach under full control to transit safely.