以下两用法均可：
一、与词形保持一致（quantity 的单复数，决定谓语动词的单复数）： 这种观点认为，不看 a quantity of 或 quantities of 后面接单数名词还是复数名词，只看 quantity 本身。即：quantity 是单数，谓语动词就用单数；quantities 是复数，谓语动词就用复数。即遵循“语法一致”的原则。例如：
A large quantity of washing machines has been sold.
A great quantity of money was spent on the project.
Large quantities of books were sent to the village schools.
Large quantities of sand were washed down the hill by the rain.
二、还有一种比较流行的观点，就是：a (large) quantity of或 (large) quantities of，其后均可跟不可数名词或复数名词。在句中作主语时，a quantity of接不可数名词时，谓语动词用单数形式；接可数名词复数时，谓语动词用复数形式。quantities of后接不可数名词或可数名词复数时，谓语动词都用复数形式。
A large quantity of washing machines have been sold.
A great quantity of money was spent on the project.
Large quantities of books were sent to the village schools.
Large quantities of sand were washed down the hill by the rain.
