The most important second generation think tank is the RAND Corporation, which was established in May 1948. Largely financed by the US Air Force, the RAND Corporation was intended to “think through the unthinkable” and to defend and promote American security interests. During this period the Hudson Institute in 1961 and the Urban Institute in 1968 were established as the second generation think tanks. 

In the beginning of the 1900s, significant think tanks were established for informing governments not only about domestic politics but also about foreign policy. These include the Russel Sage Foundation established in 1907, the Carnegie Endowment for International Peace established in 1910 by Andrew Carnegie, the Hoover Institution in 1919 by former US President Herbert Hoover, the Council on Foreign Relations in 1921, the Brookings Institution established in 1927, and the American Enterprise Institute for Public Policy Research founded in 1943.

Therefore, the correct option is C.