Don't quite understand the condition

Hi Kenken, thanks for the question The idea here is that separate sufficient/necessary statements are made. In this passage, the use of "is essential", "is required", and "is necessary" is used to indicate the necessary conditions in each statement. SE -> FNSC FNSC -> YPES YPES -> GCSP Combining all of these statements gives us: SE -> FNSC -> YPES -> GCSP The contrapositive of this entire chain is what you have written up there! ~GCSP -> ~ YPES -> ~FNSC -> ~SE Answer choice C says: No nation can have a successful economy unless at some point scientists have communicated well with the public This is diagrammed as: SE -> GCSP This is directly supported from our chain of inferences. I hope this helps. Please let me know if you have any other questions.