Which deep glacial valley in Snowdonia, described in a guidebook as 'a perfect specimen of a hanging valley', is dominated by Llyn Idwal?

• A Cwm Idwal ✓
• B Nant Ffrancon
• C Cwm Pennant
• D Cwm Llan

Cwm Idwal is a classic example of a cirque carved by glaciers, surrounded by the Glyderau peaks; Charles Darwin visited in 1831 and recognised it as a product of glaciation.