from the top of the tower, the south foot of the mountain is a sea of trees.
A. Seen
B. Seeing
C. Have seen
D. To see
网友回答
(答案→)A. Seen
B. Seeing
C. Have seen
D. To see
解析：这题考查过去分词做状语的用法：See 和主语主语the south foot of the mountain是被动关系，选A。句意是：从塔顶上看，这座山的南山角是一片树。选A。