① ____ A. In Beijing.it's 9 a.m.
② ____ B. In New York,it's 12:00.
③ ____ C. In London,it's 7 p.m.
20世纪,世界爆发了两次世界大战,比较两次世界大战,最接近的是( )
45−(45−45)= ____
(Ⅰ)求f(x)的最小正周期和最大值;
(Ⅱ)若 g(x)=f(x),x∈−π2,π2 ,画出函数y=g(x)的图象,讨论y=g(x)﹣m(m∈R)的零点个数.