Correct Answer: (d) Invasion at Pearl Harbour
Solution:Second World War began on 1ˢᵗ September, 1939 by the invasion of Germany over Poland but United States of America was not involved militarily. But, after a sudden attack of Japan at Pearl Harbour which was a naval base of United States of America, on 7 December, 1941, United States of America also participated in the Second World War militarily.