Use reasoning to answer the following question.
Keep Calm and Carry On was a motivational poster produced by the British government in 1939 in preparation for World War II. The poster was intended to raise the morale of the British public, threatened with widely predicted mass air attacks on major cities. Although 2.45 million copies were printed, and although the Blitz did in fact take place, the poster was hardly ever publicly displayed and was little known until a copy was rediscovered in 2000 at Barter Books, a bookshop in Alnwick. It has since been re-issued by a number of private companies, and has been used as the decorative theme for a range of products.\n\nBased on this passage, where did the phrase keep calm and carry on come from?

a motivational poster produced by the British government in 1939 in preparation for World War II
The relevant information to answer the above question is: Keep Calm and Carry On was a motivational poster produced by the British government in 1939 in preparation for World War II.

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So, the answer is a motivational poster produced by the British government in 1939 in preparation for World War II