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.