a quantity of和large quantities of作主语时谓语用单数还是用复数

1. 若用于a great (large, small) quantity of…结构，其后主要接不可数名词，但有时也接复数名词；这类结构用作主语时，其谓语的数原则上与其中的名词的数保持一致。如：

There are a small quantity of apples in the house. 房子里有少量的苹果。

A large quantity of food was on the table. 大量的食物摆在桌上。

2. 若该结构变成(large) quantities of…这样的形式，则当它用作主语时，其谓语动词一律用复数(与其中名词的数无关)。如：

Huge quantities of oil were spilling into the sea. 大量的石油渗到海里。

Large quantities of rice have been destroyed in the flood. 大量的庄稼在洪水中被毁坏了。

引自英语语法网：http://www.yygrammar.com/Article/201205/2946.html