Докажите, что середина отрезка с концами в точках С(a;b;c) и D(p;q;-c) лежит в плоскости ху

1...will you come, I will come if you are not busy
2.I don't like apples
3. came
4.willring you up...,come
5.will show, if you want
6.had come
7.will help, ask
8.have never seen
9.arrive
10.has stopped, is shining
11.help, will do
12.get, will get
13. what are you doing? I'm reading, I'm in a hurry,will come,i want
14.see, want
15.came, was sleeping