Letters ‘A’, ‘B’, ‘C’ & ‘D’ do not appear anywhere in the spellings of 1 to 99
Letter ‘D’ comes for the first time in Hundred
Letters ‘A’, ‘B’ & ‘C’ do not appear anywhere in the spellings of 1 to 999
Letter ‘A’ comes for the first time in Thousand
Letters ‘B’ & ‘C’ do not appear anywhere in the spellings of 1 to 999,999,999
Letter ‘B’ comes for the first time in Billion
And
Letter ‘C’ does not appear anywhere in in the spellings of entire English Counting