S, S, O, N, D etcItalian:UnoDueTreQuattroCinqueSeiSetteOttoNoveDieciECC
U (fourth, third, fourth, third, etc).
The next letter is L. Here is the sequence: a _ _ de _ _ hi _ _ lm.
D The letter sequence is the months of the year in order from January. December would end the sequence
Check out the link for the sequence.
G comes next in the musical note sequence. After G, the sequence starts again at A.
K comes next in the sequence, they are the letters on the middle row of a typewriter keyboard
I is the next letter.
The final missing letter in the sequence is d. The letters are the initials of the months of the year - the last being December.