When underway in restricted visibility, you might hear, at intervals of two minutes, any of the following fog signals EXCEPT _____________.

When navigating in restricted visibility, vessels are required to use sound signals to communicate their presence and intentions. These sound signals serve as a warning to other vessels that may be nearby and help prevent collisions when visibility is limited.

One prolonged blast is often used by vessels to indicate that they are underway, while two prolonged blasts signify that a vessel is operating in reverse. The signal of one prolonged and two short blasts is typically used by vessels to indicate a specific maneuver or action, often a request or acknowledgment of the vessel's intentions.

However, the ringing of a bell for five seconds is not typically associated with the sound signals used by vessels underway in restricted visibility. Instead, the bell signal is more relevant for anchored boats or vessels at rest, as it denotes their presence rather than their movement. In a scenario where a vessel is underway, the other signals provided are the appropriate means of communication.

Therefore, while the other sound signals are established protocols for vessels in motion, the ringing of a bell for five seconds does not apply in this context, making it the correct choice.