useful用作形容词的用法例句

　　It is a useful book and, what is more, not an expensive one.这是有用的书，更难得的是不贵。

　　The book contains much useful information.这本书包含了许多有用的.资料。

　　John always tries to cultivate people who are useful to him.约翰经常设法和对他有用的人结交。