分析完形填空的填词Mark was walking home from school one day when he n

分析完形填空的填词
Mark was walking home from school one day when he noticed a boy ahead of him.He had tripped(绊倒)and dropped all of the books he was carrying,along with some clothes,a baseball bat and a glove.Mark knelt(跪) down and helped the boy pick up the things.Since they were going the same way,he offered to carry some things for the boy.As they walked,Mark discovered the boy's name was Bill.He loved video games,baseball and history,but he was having trouble with some of his subjects.They arrived at Bill's home first.Mark was invited in for a Coke and to watch some television.The afternoon passed pleasantly with some laughs and talk.Ten Mark went home.They continued to see each other around school,had lunch together once or twice,then both graduated from junior school.Three days before graduation,Bill asked Mark if they could talk.Bill reminded Mark of the day years ago when they had first met."Did you ever wonder why I was carrying so many things home that day?" asked Bill."You see,I took away all my things from school.I had stored away some of my mother's sleeping pills(安眠药).I was going home to kill myself.But after we spent some time talking and laughing,I realized that if I had died.I would have missed so many good times.So you see,Mark,when you picked up books that day you a lot more.You saved my life"
就是问一下为什么第6行的trouble 为什么不能用problems啊?
还有第12行的stored为什么不能用put 同样都是解释为
还有为什么全篇大部分都是过去完成时啊,不是一般情况下应用过去时吗?