英语完成时 这些句子是什么用法?

题目

英语完成时 这些句子是什么用法?
课本里的：
像这句 Now in China He has found hisfamily is like a tall tree with long roots.
不能翻译成 已经 ··
1.去玩中国回来：It has been a great step for me.I have really enjoy my trip.
2.Many books have benn written about (something..)
3.If someonehas thought about a gift for me,it makes me happy
4.电影里经常出现的:you have been very helpful.
这些翻译成“完成、已经”未免太牵强了,去掉也貌似没什么说不过去的,怎么搞的吗?
考试时改卷的不分青红皂白 连might和may都不放过 别说完成时了 求以上的句子用法
考试如果出道题 ：Problem:An Internet friend ------(ask)if you could meet
怎么办?

答案

完成时是表示对现在或将来产生了影响,翻译时并不一定要翻译出来
第一句 It has been a great step for me. 表示在中国旅游我学到了一些知识,使我了解了中国.这就对我产生了影响
第二句 Many books have ben written about ... 这句话是指很多书都曾经写到过sth,而这些sth已经被读者认同或遭到批判,也有一定的影响
第三句 .If someone has thought about a gift for me, it makes me happy 如果有人想过要给我礼物的话,我会很开心. 这里的has thought or not 会影响到我的心情
第四句 you have been very helpful. 你过去对我的帮助,对我现在的生活很有帮助.这也是产生了影响
另外,在虚拟语气中,完成时就不是产生影响.
if sb had done sth,sb would/could/should have done