A. Austria
B. Poland
C. Russia
D. None of these

World War II officially began on September 1, 1939, when Nazi Germany, led by Adolf Hitler, invaded Poland. This prompted Britain and France to declare war on Germany. Germany’s annexation of Austria (the Anschluss) occurred in 1938, before the war, and the attack on Russia (Operation Barbarossa) happened in 1941, after the war had started. Thus, “None of these” is incorrect.

The correct answer to the question: "The Second World War began with Germany’s attack on:" is "Poland".