体会down的意味,“……下面”.
（来自剑桥高级学习词典）down：used,especially with prepositions,to emphasize that a place is distant from you or from somewhere considered to be central:
eg.I'll meet you down at the club after work.
on：used to show that something is in a position above something else and touching it,or that something is moving into such a position
像介词的用法,还是多背点文章、培养语感吧.