Final answer:
The attack on Pearl Harbor took place on December 7, 1941, leading to the United States' entry into World War II.
Step-by-step explanation:
The event that took place on December 7, 1941, was the attack on Pearl Harbor, option B. This was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii. It led to the United States' entry into World War II.
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