Could « c'est fou » also mean, "he's crazy" in this sentence? My answer was, "He only tells lies; he's crazy" and this was marked incorrect.
not here. he has already been mentioned--il raconte. so he's crazy has to be; 'il est fou.' "c'est fou" must be impersonal here--"that's crazy."
All right, might someone help me out with a serious question about partitive (or as choacavaco points out, indefinite) articles, please: if all he tells are lies, why is the article here des and not les?
make it about a single lie. is it A lie or THE lie? it might even be clearer in future. will he tell A lie or THE lie? the plural of 'un' is 'des'.