quantity的用法

解题思路： a large quantity of 后面跟即可加可数名词又可加不可数名词，但中心词是quantity 用作单数，large quantities 后面跟即可加可数名词（复数）又可加不可数名词，但中心词是quantities，谓语动词用复数
解题过程：
a large quantity of 后面跟什么名词？
a large quantity of 后面跟即可加可数名词又可加不可数名词，但中心词是quantity 用作单数，如
a large quantity of water is
a large quantity of books is
谓语动词是用单数
large quantities 后面跟即可加可数名词（复数）又可加不可数名词，但中心词是quantities，谓语动词用复数，如
large quantities of water are
large quantities of books are
最终答案：略