be helpful in be helpful to be helpful for 三者区别即怎么用

be helpful in +名词/动名词，表示 在···中有用，用于·····。比如：be helpful in teaching English 在教英语中十分有用; be helpful in some instances 在某些情况下很有用。
be helpful to +sb./v.，表示 对某人或某事有用，有助于····。比如：be helpful to teachers 对教师有帮助；be helpful to teaching 有助于教学。
be helpful for +sb.，表示 对某人有帮助。比如：be helpful for students to learn English 对学生学英语有帮助。

1.be helpful in doing sth.
例如We hope this leaflet has been helpful in answering your questions.
我们希望这个宣传单可以帮助您找到您想要的答案
2.it is helpful (for sb) to do sth
It is helpful to discuss your problems with your friends.
-跟你的朋友们聊聊你遇到的问题是有好处的.这里的It是形式主语,真正的主语是to后面的句子
3.be helpful for sb对某人事有益的
例如;Music with the sounds of the ocean or bird song can be helpful for some.
大海的声音或者鸟叫声对你的睡眠时很有帮助的