BOTH INTERNATIONAL & INLAND A vessel 25 meters in length must have which sound signaling appliance onboard?

Correct Answer: Option D — Whistle and bell only

Rule 33(a) states that a vessel of 12 meters or more but less than 100 meters in length must be provided with a whistle and a bell. The gong requirement only applies to vessels 100 meters or more in length, making a whistle and bell sufficient for a 25-meter vessel.