我只看了第一句话
A man buy a cat,in order to watch the cereal,if it can catch a mouse,it would be get a reward
buy显然时态不对,要用一般过去时.
一句话有多分句,至少要加个连词and
一句话中主语不统一,且it指代不明.
Once upon a time,a man bought a cat to guard the cereal well,and he promised to reward it for catching mice.