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

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

DTo see

答案：

(答案→)A. Seen

B. Seeing

C. Having seen

D. To see

解析：句意为：从塔顶往下看，南边的山脚下是一片树的海洋。本题考查分词作状语。分词作状语，其逻辑主语与句子主语一致。主语the south foot of the mountain 与see 在逻辑上为被动关系，四个选项中只有A项表被动。