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What are the difficulties that need to be paid attention to in the second volume of mathematics for three years in primary school?
1 There is a leap year every four years, such as 2004 and 2008, and the rest are normal years, 2009, 20 10, 20 1 1.
February in leap year is 29 days, and February in normal year is 28 days.
3 concept: (1) 1, 3,5,7,8, 10, wax 3 1 day is never bad.