What is the main idea of Rousseau's social and political philosophy?

I - Rousseau believed that the progress of productive forces is inevitably accompanied by the retrogression of customs and the worsening of the social and material situation of the popular masses.
II - Rousseau related the origin and increase of inequality to the appearance and development of private property.
III - Rousseau believed that the cause of social evils should be sought in the political regime.
IV - Rousseau believed that the education of children should follow the indications of nature and that corporal punishment is pedagogically harmful.
a) Only I and II are correct.
b) Only II and III are correct.
c) Only III and IV are correct.
d) I, II, III and IV are correct.