如图，边长为1的正方形ABCD的顶点A,D分别在x轴、y轴正半轴上移动，则$\overrightarrow{OB}·\overrightarrow{OC}$的最大值是（   ）

某化学兴趣小组欲检验当地石灰石中碳酸钙的纯度．在实验室将25克石灰石样品（杂质不参加反应，也不溶于水）放入盛有100克稀盐酸的烧杯中，恰好完全反应．测得烧杯中物质的总质量为116.2克．求：

①生成二氧化碳的质量．

②样品中碳酸钙的质量分数．

③所用稀盐酸中溶质的质量分数．

    Many people like to watch TV, There are all kinds of programs on TV. The soap opera is one of them.

    The soap opera was first on the radio in the 1920s, then it started on TV in the 1940s. Why do so many people like to watch soap operas on TV, especially young people? What makes soap operas popular? Let's find out.

    First, what's happening in the soap opera is very different from our lives. Everything is perfect in the play, People don't need to worry about almost anything. People don't have more Problems.

    Second, there are many beautiful girls and handsome boys in the soap opera. They are cool. They make young people crazy. They make young people happy.

    Third, the story in the soap opera is usually interesting. It makes people relaxed after a day's hard work. Even some old people like to watch it, too.

    But some people don't like it, they think the show is too slow and too long. Do you like to watch soap operas? What do you think of them?