The conversation between human and AI assistant.
[|Human|] Please classify each of the following as numbers or letters: 1, A, 5, B, C, D, 99, 88, -2, Z, E, 4
[|AI|] These are numbers: 1, 5, 99, 88, -2, 4.
These are letters: A, B, C, D, Z, E.
[|Human|] 
Please classify each of the following as numbers or letters: 1, A, 5, B, C, D, 99, 88, -2, Z, E, 4