GWD13语法还有两个问题，望帮助

Q30:

For the first time in the modern era, non-Hispanic Whites are officially a minority in California, which amounts to a little less than half the population of the state, down from nearly there-quarters only a decade ago.

Q30:

For the first time in the modern era, non-Hispanic Whites are officially a minority in California, which amounts to a little less than half the population of the state, down from nearly there-quarters only a decade ago.

为何不选E却选D？

－　a decade ago 是时间状语，不可以直接修饰名词 three-quarters.

Concerns about public health led to the construction between 1876 and 1904 of three separate sewer systems to serve metropolitan Boston.

1. Concerns about public health led to the construction between 1876 and 1904 of three separate sewer systems to serve


2. Concerns about public health have led to the construction of three separate sewer systems between 1876 and 1904 to serve


3. Concerns about public health have led between 1876 and 1904 to the construction of three separate sewer systems for serving


4. There were concerns about public health leading to the construction between 1876 and 1904 of three separate sewer systems serving


5. There were concerns leading between 1876 and 1904 to the construction of three separate sewer systems for serving

－　C中没有明确的时间状语需将一般过去式改成现在完成时；between 1876 and 1904的修饰对象改变了。名词 + of 结构中可以插入状语修饰成分。－偶记得大全里有类似的题目的。

为何不选C却选A。construction of 不应该分开呀？

Q30:

For the first time in the modern era, non-Hispanic Whites are officially a minority in California, which amounts to a little less than half the population of the state, down from nearly there-quarters only a decade ago.

1. which amounts to a little less than half the population of the state, down from nearly three-quarters only a decade ago
2. which amounts to a little less than half the population of the state, down from a decade ago, when it was nearly three-quarters
3. and that amounts to a little less than half the population of the state, down from a decade ago, when they were nearly three-quarters
4. amounting to a little less than half the population of the state, down from nearly three-quarters a decade ago
5. amounting to a little less than half the population of the state, down from what it was a decade ago by nearly three-quarters

为何不选E却选D？

参考了一下其它网友的意见，这题应该选D。
1.　E中it指代不清，前面有好几个单数名词。

2.　还有刚刚想到的what it was应该可以省略，似乎跟状语从句的省略方式一样，为简洁。－－这点请NN们确认。

3.　原来说D错的时候是应该a decade ago的问题，偶现在想应该看成是时间状语放在句末的用法。

我当时选E的原因是E的表述很完整down from what it was a decade ago by nearly three-quarters  “down from...by....” ;而 D down from nearly three-quarters a decade ago    “down from +数量” 变成了从什么数量开始下降。。。似乎不对诶

请指正

msfox讲得有道理，E改变了句意。

从原句的表述来看，句子的意思是non-Hispanic Whites人口的数量从原来占加州人口总数的四分之三降到现在的不到二分之一。

down from...：从......开始降;

down from...by...：从......开始降多少。

所以E选项的意思是从原来的数量降了四分之三。

嗯

明白了les好强的说

here, 'amounting to' is employed to modity the entire, preceding sentence, while 'which' should not be used in this way.

D. amounting to a little less than half the population of the state, down from nearly three-quarters a decade ago

E. amounting to a little less than half the population of the state, down from what it was a decade ago by nearly three-quarters

我<<还是觉得你(E)最好>>  first, D 会不会有歧义啊, from nearly three-quarters a decade ago 会不会被认为是 10 年前就 down 了 3 quarters 了?   Secondly, D 似乎没有说从哪个基准降了 3- quarters, 好象令人难一接受...  而E 解决了这些问题.   

仅供参考, 请指正.