原句少了一个are吧（not前）,这里是一个结构问题, be of +抽象名词=be +形容词,of high enough quality其实就是qualified的意思,表示“高质量的”,(这个地方的学校质量不够高,难以满足他们的需求）再如
He is of great help= He is very helpful
The English learning is of great importance=The English learning is very important