Waste can be seen everywhere in the school. Some students ask for more food than they can finish and others often forget to turn off the lights when they leave the classroom. They say they can afford these things. But I don't agree with them.

    Waste can bring a lot of problems. Although China is rich in some resources, we are short of others, such as fresh water. It is reported that we will have no coal or oil to use in 100 years. Think about it. I think we should say no to the students who waste things every day. Everybody should stop wasting as soon as possible.

    In our everyday life, we can do many things to prevent waste from happening. For example, turn off the water taps when we finish washing, turn off the lights when we leave the classroom and try not to order more food than we need. Little by little, everything will be changed. Waste can be stopped one day if we do our best to form the habit of saving.

①卤水中含有MgCl₂、KCl和MgSO₄等物质，如图是三种物质的溶解度曲线．t₂℃时，三种物质的饱和溶液中，溶质质量分数最小的是____．

②将t₂℃时三种物质的饱和溶液加热到t₃℃以上时，仍然为饱和溶液的是____．

③将饱和氯化镁溶液由t₃℃冷却至t₁℃，下列四种叙述中，正确的是____（填序号）．

Ⅰ．溶液的质量不变Ⅱ．氯化镁的溶解度变小

Ⅲ．溶液中溶质质量不变Ⅳ．溶液中溶质质量分数变小

④在t₃℃时，60克KCl的饱和溶液与60克MgCl₂的饱和溶液中，溶质MgCl₂与KCl的质量比为3：1，则t₃℃时MgCl₂的溶解度为____．

照样子，写词语。

黑漆漆      ____ ____ ____ 

结结巴巴    ____ ____ ____