求助两道GWD13套语法题，我实在是想不明白啊

CoralOcean

Q8:

A new hair-growing drug is being sold for three times the price, per milligram, as the drug’s maker charges for another product with the same active ingredient.

 

1. as
2. than
3. that
4. of what
5. at which

给出的答案是D,谁能告诉我为什么是D吗，E为什么不对啊？

Q15:

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

答案是A, 可是我觉得B更符合语法结构，谁能解释一下A对的理由好吗？

800liang

the price of what从句.what 从句相当于名词

between 1876 and 1904明确的过去时间一般过去时

crystalflame

我懂了，谢谢解答！