On Inland Waters, two power-driven vessels have reached a passing agreement via VHF radiotelephone in an overtaking situation. Under Rule 34, which statement is correct regarding whistle signals?

1. A. Whistle signals are still mandatory and must be exchanged regardless of any prior VHF agreement.
2. B. The vessel being overtaken must still sound a confirmatory whistle signal even if VHF agreement was reached.
3. ✓ The vessels are not obliged to sound the prescribed whistle signals but may do so; if agreement is not reached, whistle signals shall be exchanged and shall prevail.Correct
4. D. VHF agreement is not recognized under Rule 34 and has no effect on the requirement to exchange whistle signals.