of+n.(抽象名词）=adj.(形容词）通常可以跟在be动词后面.They are always of good quality.那些东西总是质量优质的（质量好的）.
举个例子吧.I will be a man of use.=I will beoa useful man.我将做一个有用的人.
The meeting is of importance.=The meeting is very important.这个会议非常重要.
Products of good quality always sells good.优质产品总是畅销的.（of+n.修饰产品Products）