用括号内所给单词的适当形式填空,必要时可加助动词或情态动词。
Waste can be seen everywhere in our school. Some students ask for more food than they can eat and others often forget____ (turn)off the lights when they leave the classroom. They say they can afford these things. But I____ (not agree)with them.Waste can bring a lot of problems. Although China is rich in some resources (资源), we're short of others, for example, fresh water(淡水). It____ (report) that we will have no coal(煤) or oil to use in 100 years. So if we go on____ (waste) our resources,what can we use in the future? Think about it. I think we should
say to the students who waste things every day. Everybody____ (stop) wasting as soon as possible.
In our everyday life, we can do many things____ (prevent) waste from happening, turn off the water taps(龙头) when we____ (finish) washing, turn off the lights when we leave the classroom, try not to order more food than we need, and so on. Little by little, everything will be changed. Waste can be stopped one day if we do our best.

（Ⅰ）化C₁，C₂的方程为普通方程，并说明它们分别表示什么曲线；

（Ⅱ）若C₁上的点P对应的参数为t=﹣ $\frac{\pi }{2}$ ，Q为C₂上的动点，求线段PQ的中点M到直线C₃：ρcosθ﹣ $\sqrt{3}$ ρsinθ=8+2 $\sqrt{3}$   距离的最小值．