Two power-driven vessels have reached a passing agreement by radiotelephone in a head-on situation on inland waters. Which statement is correct regarding whistle signals under the Inland Rules?

1. A. Whistle signals are still mandatory and must be exchanged before any maneuver is executed.
2. ✓ The vessel is not obliged to sound whistle signals but may do so; if agreement was not reached, whistle signals shall be exchanged and shall prevail.Correct
3. C. Whistle signals are prohibited once a VHF agreement has been reached to avoid confusion.
4. D. Only the stand-on vessel is relieved of the obligation to sound whistle signals.