How do you trill a low C on a flute?
For the lower C to D, you use the first trill key with your index finger. For the C to D up the octave, it's the other trill key - with your ring finger.
For the lower C to D, you use the first trill key with your index finger. For the C to D up the octave, it's the other trill key - with your ring finger.