科学兴趣小组在调查一化工厂时，发现有个车间排出的废水澄清透明，呈黄色．为测定该废水中所含的物质，他们进行如下实验（假设能发生的反应均恰好完全反应）：

①用pH试纸测试，测得pH为2．

②取一定量废水溶液，加入Ba（NO₃）₂溶液，无现象．

③另取一定量废水溶液，加入AgNO₃溶液后，过滤，得到白色沉淀A和滤液．

④向滤液中加入NaOH溶液，得到红褐色沉淀B．

由此可知：该废水溶液呈____性；所得的红褐色沉淀B为____；废水溶液中肯定含有的盐是____．

设$f\left(x\right),g\left(x\right)$分别是定义在R上的奇函数和偶函数，当$x<0$时，$f^{\text{'}}\left(x\right)g\left(x\right)+f\left(x\right)g^{\text{'}}\left(x\right)>0$，且$g\left(-3\right)=0$，则$f\left(x\right)g\left(x\right)<0$的解集是（    ）

    Tomorrow is the Dragon Boat Festival. In the morning, I will visit my grandparents with my father and mother. My grandma will make zongzi for us. I like sweet zongzi with Chinese dates (枣). My parents like salty (咸的) zongzi with meat. My grandpa will cook a big lunch for us. In the afternoon, I will watch the dragon boat races with my friends. What a nice day!