A:统一度量衡和货币
B:焚书坑儒
C:建立中央集权制度
D:修筑长城
将2个相同的a和2个相同的b共4个字母填在3×3的方格内,每个小方格内至多填1个字母,若使相同字母既不同行也不同列,则不同的填法种数为 ( )
①﹣3是函数y=f(x)的极值点;
②﹣1是函数y=f(x)的最小值点;
③y=f(x)在x=0处切线的斜率小于零;
④y=f(x)在区间(﹣3,1)上单调递增.
则正确命题的序号是____.
-- It seems that you know a lot about the story.
-- Well. I ____ (read) it many times.
My mother is a teacher.She goes to school 7:00 the morning.