Which German-born physicist, who became a U.S. citizen in 1940, developed the theory of relativity and warned President Roosevelt about the potential of atomic weapons?

• A Niels Bohr
• B J. Robert Oppenheimer
• C Richard Feynman
• D Albert Einstein ✓

Einstein fled Nazi Germany in 1933 and settled at the Institute for Advanced Study in Princeton, where he worked until his death in 1955.