六、third largest whether to，stopped,going both and，hard，win,happened to，produces，without saying,owner，unless helps

七、77。didn't 78.himself 79。spend 80。on 81。tell

82。what 83。listening 84。more 85。carefully 86。then

八、Possible version

We are studying in this school。It’s not good to spit in public places，such as in the library and in the classroom。We should neither draw pictures on the walls nor throw any litter onto the ground.I think we should make it a rule to so some cleaning every day。If everyone tries his best to do something useful for our school,I'm sure our school will become more and more beautiful。That’s all，thank you！