Which fiord in New Zealand's South Island, a major tourist destination, is technically classified as a sound rather than a true fiord in some geological definitions?

• A Milford Sound ✓
• B Doubtful Sound
• C Dusky Sound
• D Fiordland's coastline generally

Milford Sound (Piopiotahi) is actually a fiord carved by glaciers, despite "Sound" in its English name.