请教95-8-9

9 _____ at a river ford on the Donner Pass route to California, the city of Reno grew as bridges and railroad were built.

(A) Settle

(B) To settle

(C) It was settling

(D) Having been settled

答案：D.

分析：逗号后面为中心句，故逗号前面为从句或非谓语动词充当的状语。且主语city与动词settle为被动关系，故A、B、C都可被排除。

翻译参考：由于位于通往加利福尼亚路线上D的一个河滩，R城市随着桥和铁路的建立发展起来。

难度：2

通过排除法选的D，但是还是不明白为什么要用having ，请指教。谢谢。

Having been settled表示 be settled 这个动作发生比主句动作were built 早 也就是说be settled

后 才 were built

没什么特别