When approaching another vessel in a bay, if you fail to understand the intentions of the other vessel or doubt whether sufficient action is being taken to avoid collision, what sound signal must you give under RIPA Rule 34(d)?

1. One prolonged blast every five minutes
2. Two prolonged blasts followed by one short blast
3. At least FIVE short and rapid blasts on the whistle or horn (señal de peligro / duda)
4. Continuous ringing of a ship's bell for two minutes