by thick bamboo and high forest the ancient city hadn’t been discovered until the 1990s.

问题补充：

by thick bamboo and high forest, the ancient city hadn’t been discovered until the 1990s.

A. Surrounding

B. Surround

C. Surrounded

D. Having surrounded

答案：

A. Surrounding

B. Surround

(答案→)C. Surrounded

D. Having surrounded

解析：动名词表示主动意思，过去分词表示被动含义，这里有被竹子及高树环绕的意思所以选B。被浓密的竹子和高大树木环绕，……