1)to do 表示将做什么的或用以做什么的. 只能作后置定语. 例如: He is the boy to come. They have no food to eat. 2)ing形式 表主动或正在进行. 单个词置前,词组置后. 例如: Do you know the sleeping boy? The boy lying on the grass looks like my friend. 3)ed形式 表被动或完成.单个词置前,词组置后. 例如: This is a used book . The book given to him is an English novel .