1 which said,'Anyone who leaves litter in these woods will be porsecuted!'
这一长段话是一个定语从句，修饰前面的sign。
2 .'Anyone who leaves litter in these woods will be porsecuted!'
这一句话中WHO后面又是一个定语从句。
3 这个定语从句，拆分成两句话如下：
Anyone leaves litter in these woods.
Anyone will be porsecuted!
不能不用WHO
直接Anyone leaves litter in these woods will be porsecuted是不可以。因为同一个简单句里面出现了两个谓语动词（leaves和 will be porsecuted）。 加一个who就成为定语从句了。
4 'Anyone who leaves litter in these woods will be porsecuted!不是一个主语从句，而是一个定语从句。who leaves litter in these woods是从句，修饰anyone.
5 主语从句可以前面用THAT引导， 比如 The news that Tom is now in our school is not true. (明星)Tom现在就在我们学校的新闻，不是真的。
6 that anyone leaves litter in these woods will be porsecuted!这样不可以的。谁是主语呢？that又是指代什么呢？ 哈哈！
勤学好问 天天进步！
