a mass of/masses of，an amount of/amounts of, a good supply of/ supplies of, an abundance of加名词时谓语动词的选择由量词的单复数决定。其中amount只修饰不可数名词，mass, supply, abundance可数和不可数名词均可修饰。
例如：There is a mass of boys in the yard.
There are masses of ice in the river。
这体现的主谓一致原则中的语法一致: 谓语动词单复数完全由主语决定
