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.
Agreatquantity of moneywasspentontheproject.
Large quantities of booksweresenttothevillageschools.
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)quantityof或(large)quantitiesof，其后均可跟不可数名词或复数名词。在句中作主语时，aquantityof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。quantitiesof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.
Agreatquantity of moneywasspentontheproject.
Large quantities of booksweresenttothevillageschools.
Large quantities of sand were washed down the hill by the rain.