a large quantity of作主语时,谓语单复数不是由of后的名词决定的,
而是由quantity的单复数来决定的.
a large quantity of 大量的（用于可数或不可数名词）,谓语用单数
large quantities of 大量的（用于可数或不可数名词）,谓语用复数
如:A large quantity of beer was sold.
售出了大量的啤酒.
Large quantities of water are needed for cooling purpose.
冷却要用大量的水.