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
网友回答
(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。