如图，已知函数 $y=-\frac{1}{2}x+b$ 的图像与x轴、y轴分别交于点A、B，与函数 $y=x$ 的图像交于点M，点M的横坐标为2．

阅读理解

    I went on vacation with my family last summer. “Wake up! It's time to go fishing,” My mom woke me up. After having breakfast we got on a boat. Getting up at 6 a.m. was really early and I was not happy, but later, I had fun.

    My uncle caught (抓住) a big fish first. And my mom caught one, too. Then I caught a Black Drum. Next, my dad caught a big Sheepshead. The captain said no one caught a big fish like this one. We were all happy when we heard this. Later we tried to catch small sharks (鲨鱼). My grandpa caught one, but it snapped the line (咬断绳子). My uncle caught one, but it also snapped the line. My dad caught one at last. It didn't look so scary but was a little funny.

    Then our fishing activity was over, and we went back with all the fishes. We were tired but happy!

一物体作匀加速直线运动，通过一段位移△x所用的时间为t₁，紧接着通过下一段位移△x所用时间为t₂．则物体运动的加速度为（　　）

如图，轻质杠杆可绕O点转动，杠杆上吊一重物G，在力F的作用下杠杆在水平位置静止，L为F的力臂，请作出力F的示意图．

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近年来，“晒黑族”异军突起，他们将社会上的不平事在网上进行披露，以警醒其他网民或政府部门，推动问题的解决。“晒黑族”的一个口号就是：“只有不想晒的，没有不能晒的。”对“晒黑族”的行为认识正确的是( )
①拓宽了公民直接管理国家事务渠道
②有利于改进政府工作，维护社会正义
③是公民参与民主决策的途径，是社会进步的表现
④必须坚持权利与义务统一的原则，做到有序参与