GWD13语法还有两个问题，望帮助

dhhgh11

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.

A. which amounts to a little less than half the population of the state, down from nearly three-quarters only a decade ago

B. which amounts to a little less than half the population of the state, down from a decade ago, when it was nearly three-quarters

C. 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

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

为何不选E却选D？

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

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

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

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

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

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

为何不选C却选A。construction of 不应该分开呀？

mjiirggh

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.

A. which amounts to a little less than half the population of the state, down from nearly three-quarters only a decade ago

B. which amounts to a little less than half the population of the state, down from a decade ago, when it was nearly three-quarters

C. 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

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

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。