Set A={F,L,W,O} which of the following is not a Set-builder form for set A?

Options

A. {x , x is a letter from the word 'FOLLOW'}
B. {x : x is a letter from the word 'FLOW'}
C. {x , x is a letter from the word 'WOLF'}
D. {x : x is a letter from the word 'SLOW'}