一篇短文改错,有些不明白的地方,呵呵

一篇短文改错,有些不明白的地方,呵呵
One day,some children were playing hide-and-seek 正确
in an garden.The garden was big and full of man-made an－》 a
stones.The children knew them very well because them－》it
they played there very often.Then,the youngest of 正确
them saw a tall jar,and had an idea.He decided climb decided 后加 to
into it and hide himself.However,it was filled of fill － 》with
waters.As soon as he got into it and began to waters－》 water
drown,he let out a cry of help.When all were frightened,of －》 for
one of their picked up a stone and threw it hard at their －》 them
the jar.The jar was broke and the boy was saved.broke－》broken
问几个小问题
1）第5行 and后不加主语没关系么?我只知道要没逗号主语一致可以.但这里有个逗号～
2） full of 是不是就等于 fill with啊.既可以说This jar is full of water.也可以 This jar is fill with water.
3） he let out a cry of help.这句话中为什么of改成 for?of for from at都有因为的意思.但是为什么这里用for?其它的不可以
如果可以麻烦讲讲四种因为是靠什么区分的,什么情况用什么.赶紧不仅.
主要全篇文章就是第三个这里这个知识点不明白,真相弄明白啊～