The correct answer is C. Both believed that societies were built upon social contracts.
Hobbes and Rousseau are both contractual philosophers of the Enlightenment period. They both deal with human nature, the origin of society, and how society should be ordered.
On one hand, Thomas Hobbes in his book, Leviathan, argued that after a chaotic state of nature, individual humans would organize, make a social contract, and renounce to some individual liberties in order to form a strong central power (the state) that protects them from the abuse of stronger individuals.
On the other hand, Jean-Jacques Rousseau said in the political treaty The Social Contract, that during the state of nature the individual human was naturally good but it was impelled to associate to others in order to satisfy its needs. For that reason, humans would freely make a social contract by which they would be led by the general will of the society, which is fundamentally a democracy.
