You are approaching the first of two drawbridges that span a narrow channel. The second drawbridge is close to the first. Which signals should you sound?

A
Sound the request-for-opening signal for the first bridge only, who will notify the second bridge of your approach
B
Sound the request-for-opening signal twice in succession to indicate you must pass through both bridges
C
Sound the request-for-opening signal, pause for about 10 seconds, then sound two prolonged blasts.
D
Sound the request-for-opening signal and, after the bridge acknowledges it, sound the request-for-opening signal for the second bridge.
E