f(x)=ax+2a+1,在[﹣1,1]上f(x)的值可正可负,则实数a的范围是( )
(﹣1,﹣)
翻译下列短语。
1. walk to school ________________________________
2. look at a picture ________________________________
3. play checkers ________________________________
4. talk to my teacher ________________________________
5. have a nice trip ________________________________
简述物流信息管理的主要内容。