We have a big playground in our school .We all like to 1 games 2 after school .It's Friday .We have only two classes 3 the afternoon . 4 school is over（结束的）,a lot of students go to the playground quickly.  The boys of Grade Two often 5 soccer. The girls like 6 them playing .Soccer is their favorite sport . Their teacher Mr Li also 7 football. Li Ming , Li Lei and Wei Fang are students of Grade One .They sometimes play 8 the students of Class Two. It’s half past five 9 . It's time 10dinner . My father is waiting for me at the school gate .

“与善人居，如入芝兰之室，久而不闻其香，即与之化亦。与不善人居，如入鲍鱼之肆，久而不闻其臭，亦与之化亦。”古人这句话告诫我们要（  ） 

如图是一个半圆，求它的周长的正确算式是（  ）

已知a∈R，若关于x的方程x²+x+|a﹣$\frac{1}{4}$|+|a|=0有实根，则a的取值范围是____