A
这是作状语的分词短语,逻辑主语是句子的主语 the south foot of the mountain .
用现在分词作状语的情况：
如果句子的主语是作状语的分词短语所表动作的执行者,用现在分词
如：
Sitting at the back of the classroom,he can't see what's on the blackboard clearly.
而如果句子的主语是作状语的分词短语所表动作的承受者,用过去分词
如：
Seen at the top of the mountain,the school looks more beautiful.