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 the spellings of entire English Counting...

Just Try...

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