The correct answer is Option 3) i.e. Both A and C are correct Sentence A) The Founding Fathers were not unaware of the possibility that a demagogue or a knave might win the presidency. Here use of knave is correct. Knave means a tricky deceitful fellow Sentence B) Despite the scandals and bad press plaguing the company, Facebook has a knave of continuing to grow both users and revenue. Here use of Knave makes no sense. 'Knack' should be there in place of 'Knave'. Knack means a clever way of doing something Sentence C) Anyone who has observed both major parties over the decades knows that each party has its share of fools, knaves, and outright crooks. Here use of Knave is correct. Knave means a tricky deceitful fellow So sentences A and C are correct