短文填词根据短文内容和以下提示：1)首字母提示，2)语境提示，3)汉语提示。在每个空格内填上一个适当的英语单词。所填单词要求意义正确，拼写准确。
       We are students of No. 10 Middle School. Recently we have____ (拜访) a paper factory. The paper factory is ____  to the river which gives us ____ (饮用)water. But we found that the factory was p____  waste water directly into the river. Now the water in it is very dirty. Lots of fish have  ____ . Some farmers say that some of their  ____  (羊) and cows have become____   and some have already died ____  they drank the water from the river. So we are  ____  to you to see if you can do something about this. We think the  ____ (污染) must be stopped right now. Thank you!
Yours sincerely，
Mike and John

如图所示的滑轮组提升重物，请画出最省力的绳子绕法。

教室里有红黄蓝三盏灯，只有一个拉环，拉一次红灯亮，拉两次亮红灯和黄灯，拉三次三灯全亮，拉四次全部灭，现有编号1到100的同学，每个同学拉开关拉自己编号次灯．比如第一个同学拉一次，第二个同学拉两次，照此规律一百个同学拉完灯的状态是____ ．