a mass of 谓语单数还是复数

　　Her arm was a mass of bruises.

　　她的胳膊上伤痕累累。

　　Her hair was a mass of tangles.

　　她的头发乱糟糟的。

　　On his desk is a mass of books and papers.

　　他的书桌上有大堆的书籍和文件。