题目：Today, because of improvements in agricultural technology, the same amount of acreage produces double the apples that it has in 1910.

A.  double the apples that it has

OG解释：the adjective double cannot modify the verb produces, only an adverb(twice) can modify a verb.

但是我查朗文词典，里面double 有名词，动词，形容词和副词四个意思，

其中第四个的例句是：the recipe said two cupfule of milk, but I used double that amount.

第一个名词的例句是：Normally it only costs 3 pounds to get in, but because it was a Sunday I had to pay double.

请问各位大师到底我该怎么理解？

至目前為止，我所總結的OG的用法。     

         Double (adj)，是”前置”限定詞，必須有一個清楚的修飾對象，並且不能和其所修飾的對象有間隔，必須緊鄰在限制對象之前。(OG 4)

Be double the amount of ……

Be double the figure in 1977.

Be double what it is ……

Twice(adv)，修飾動詞，因此可以和所修飾的動詞之間有所間隔，習慣用法        

如下： I do twice as much (adj./adv./ n.) as you do.

              The same amount of acreage produces twice as many apples as it did in the past.(OG128)

              Do twice the amount that+子句/ twice what子句

Four times as many more Americans were killed in the fought at   (OG37)

Sharpsburg as (those who可省) would later be killed on the beaches of Normandy.

Dirt roads cost twice as much to maintain as paved roads do (cost to maintain). (OG85)

也有相同的疑问，楼上的总结是不错，问题是double做副词也有双倍的意思，那么如何判断这道题上

的double 是形容词还是副词呢？？

我的理解是：

1)double作形容词放在名词前，修饰名词。同理放在名词前的double应该是属于形容词类

2)double作副词修饰动词时，后面不接名词。

3)double作名词时前面需要有限定词来修饰，如a；

  在及物动词后充当宾语；惯用语如on the double...

ouble的意思是加倍，但是他并不一定指定是数量的增大还是体积或者其他。

在本句中'produces double the apples'其实无法说明到底是数量的增加还是苹果size的增大。

但是如果使用twice就明确是指数量。

我理解wuyan的第二条就是：

double如果作副词的话,需要遵循一定的语序：v. + n. + adv. 或者 adv. + v. + n.

我所有的语法都参照朗文当代第四版（电子版）...double作adv.只常见于固定搭配的短语，例如bent

double,see double，没有后接名词的举例。