from the top of the tower the south foot of the mountain is a sea of trees. A. SeenB. See

问题补充：

from the top of the tower ,the south foot of the mountain is a sea of trees.

A. Seen

B. Seeing

C. Having seen

D. To see

答案：

(答案→)A. Seen

B. Seeing

C. Having seen

D. To see

解析：句意为：从塔顶上看，这座山的南山脚下是一片树的海洋。此处为非谓语动词作状语，在此考点中应找到非谓语动词的逻辑主语，即句子的主语为非谓语动词的逻辑主语，然后判断两者之间的关系，即主被动和时间关系。此题中句子的主语是the south foot of the mountain与see之间的关系为被动，故为seen, 所以答案应为A。