1.be useful to_______ 2.be helpful to______3.be important to______4.be necessary to______
问题描述：
1.be useful to_______ 2.be helpful to______3.be important to______4.be necessary to______
填doing或do
答
be useful to do sthit is helpful to do sth.做……是有好处的It is helpful for sb.to do sth.某人做……是对他有好处的这两个都是it 做形式主语helpful 是表示“有好处”,而不是“有助的” it is helpful in doin...