Which of the following events started the armed conflict in Europe in 1939?
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A. Britain sent tanks to defend Denmark.
B. The Soviet Union attacked Germany.
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C. Germany invaded and occupied Poland,
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D. Germany used bombers to attack Britain.

What is the main difference between primary and secondary sources? a. primary sources are historical documents, and secondary sources are modern-day documents. b. primary sources are derived from museums and archives, and secondary sources are created by history students and academics. c. primary sources are found in ancient places with a rich history, and secondary sources are found in historical journals and blogs. d. primary sources are created during a particular historical era, and secondary sources are created by studying primary sources.