in oder to do that, the black c pawn should be on c4 instead then it would be possile to do the en-passant cxb3 if white has move b4.
Why c x b is an illegal move?
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How did you get your rating without know this while millions of avid fans who study endlessly everyday can not achieve what you have? The injustice of this world has lead me to quit chess forever, because of this!
Look up the rules of En passant.