解答如下：

(1)a quantity of +不可数名词（单数），作主语，谓语用单数

 A large quantity of beer was sold.  
售出了大量的啤酒.

A large quantity of water is stored in the reservoir. 
水库存了大量的水.

(2)a quantity of +可数名词（复数），作主语，谓语用复数

There are only a small quantity of flowers left in the garden.  
花园里只剩下少量的花了.

(3)quantities of +名词，作主语，谓语用复数

Small quantities of poison were detected in the dead man's stomach.
在死者胃中找到了少量的毒药。

(4)in quantity 在数量上，大量/ in large quantity大量

After some initial problems, acetone was successfully produced in quantity.  

解决了最初的一些问题之后，终于成功地制造出了大量丙酮。

Ores are also being obtained in quantity from other countries.  

矿石也从国外大量输入.

It's cheaper to buy goods in quantity / in large quantities.  

大批量购货较便宜.

If anything gains in quantity, it must lose in quality.  

在量上有所得, 在质上必有所失.

备注：

(1)a quantity of +名词。作主语，由介词“of" 后面的名词是可数名词还是不可数名词来确定谓语的单复数。

(2)quantities of +名词，作主语，因量词已经为复数形式，则后面名词无论是为可数还是不可数，其谓语动词都为复数形式。

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