[求助]GWD6-17

zhangzhiming

Q17:

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

The answer is A, but I chose C, what's the problem?

himba

C时态错，发生在1876到1904的事应该是过去时；between 1876 and 1904位置错，把led to分开不好；for serving不如to serve好，construction的目的是服务于Boston，要用不定式to do表目的。