be useful to造句：
1、This reference book is very useful to our study。這本參考書對我們的學習很有用。
2、We all know trees are very useful to human。我們都知道樹對人類很有用。
3、The canal has proved useful to the county in many ways。這條運河在許多方面對這個縣很有用。
be useful for造句：
1、 It is very useful for a person to know how to swim。對一個人來說，學會游泳是非常有用的。
2、The book is useful for making sentences。這本書對造句很有用。
3、 I think it would be useful for you to learn the basics of marketing。我認為學習市場營銷的基礎知識對你很有用。