设变量x，y满足约束条件$\left\{\begin{array}{c}x-y\ge -1\\ x+y\le 4\\ y\ge 2\end{array}\right.$,则目标函数$z=2x+4y$的最大值为（   ）

在生物实验设计中，下列不能作为一组对照的是（　　）

完形填空

　  All my life people have told me that I was bright and that I had a lot of potential. I usually did really 1in school and I even got a scholarship to a really good2．The only thing that I wasn't good at was 3friends. I was so shy that I had a hard time talking to people.I just didn't 4anywhere.

      Then it all changed.I started 5classes, getting into trouble and then I was6out of college. I started7with the other kids I grew up with that didn't have the same8I had.We lived in poor neighborhoods and we had no idea how much our 9couldaffect our future.We weren't kids anymore and the only thing we 10was the streets. I was looking up to the11people and I couldn't even recognize myself12．Tomake a long story short, I went to prison.Twice. I 13thought I would make it to see my family again, 14I did.

        Now I'm with my 15．I never cried through any of it, not even when I was in the hospital or in16．I suddenly felt so17to be home. My heart finally opened up and that 18of being abandoned was gone.All I want to do now is give to other people the19way I know now.Just decide who you want to be 20someone else decides foryou.

Netes：

potentialn．潜力

①小红学习非常克苦，直得大家学习。____

②小方题出了两个问提．____

③虽然山村条件坚苦，但王老师扔然尖持留下来。____

④这是一为慈详的老人。____

⑤云南石林的石头形壮非常其特。____

⑥篮天上漂着朵朵白云。____

⑦撒水车正在忙碌地工做．____

⑧国防军人正用实际行动宝卫着组国。____