诗歌鉴赏。
                                                                                                   望岳
                                                                                             （唐）杜甫
                                                                  岱宗夫如何? 齐鲁青未了。造化钟神秀，阴阳割昏晓。
                                                                  荡胸生曾云，决眦入归鸟。会当凌绝顶，一览众山小。

根据图中小磁针N极指向，标出磁体的N极和S极，并画出磁感线的方向。

肺与外界气体交换的过程