A lot of research and studies have shown that Trench oil, taken out from kitchen waste, ______ the increase of cancers. [      ]

A.  results from  

B. attends to    

C. contributes to    

D. devotes to

一般在城市建设初期可采用（）给水管网。

a、环网状

b、平行式

c、垂直式

d、树枝状