Final answer:
c. The attack on Pearl Harbor by Japan sparked the end of America's isolationist policy and led to the U.S. entering World War II.
Step-by-step explanation:
c. The end of America's isolationist policy was sparked by the attack on Pearl Harbor by Japan. On December 7, 1941, Japan launched a surprise attack on the U.S. naval base at Pearl Harbor in Hawaii, leading to the U.S. declaring war on Japan and entering World War II.
This event was the catalyst for America's entrance into the war, and it marked the end of the country's isolationist policy.