be useful to造句：

　　1、This reference book is very useful to our study。這本參考書對(duì)我們的學(xué)習(xí)很有用。

　　2、We all know trees are very useful to human。我們都知道樹對(duì)人類很有用。

　　3、The canal has proved useful to the county in many ways。這條運(yùn)河在許多方面對(duì)這個(gè)縣很有用。

　　be useful for造句：

　　1、 It is very useful for a person to know how to swim。對(duì)一個(gè)人來(lái)說，學(xué)會(huì)游泳是非常有用的。

　　2、The book is useful for making sentences。這本書對(duì)造句很有用。

　　3、 I think it would be useful for you to learn the basics of marketing。我認(rèn)為學(xué)習(xí)市場(chǎng)營(yíng)銷的基礎(chǔ)知識(shí)對(duì)你很有用。