be of
具有...性质,内容
e.g.
Perhaps this book will prove to be of some use to you in your studies.
也许这本书会对你的研究有用处.
I was glad to be of some assistance.
我很高兴为您效劳.
只能接名词,在网上又给你找了一份更详细的,你去看看吧.