The Great Wall to be the longest wall in the world runs across China like a huge dragon

问题补充：

The Great Wall, to be the longest wall in the world, runs across China like a huge dragon．

A. saying

B. to say

C. said

D. being said

答案：

A. saying

B. to say

(答案→)C. said

D. being said

解析：考查过去分词作定语。said 在这里相当于which is said,句意：在世界上被认为最长的长城横跨中国就像一条巨龙一样。故选C。