Thanks for the help

Allie I started on the standard keyed 'silver' flute and then moved on to wooden flutes. Unfortunately my wooden flute has a nice tone but doesn't go below D, it was all I could afford and I had to compromise on something and that was to lose the low C for reasons of cost

I don't really understand harmony and Helen answered the question I should have asked. When joining in I played the D instead of B and it didn't seem out of place, just didn't understand why. The low bit of the tune is one of its best bits so yes it would probably change the overall sound in a bad way if I jumped octave at that point.
Thanks everyone, now if I could just understand what 3rds and 5ths are!

Roger