读图回答，目前人类活动对水循环的影响环节及办法主要表现在(　　)

有3个正方形如图所示放置，阴影部分的面积依次记为S₁，S₂，则S₁：S₂等于（  ）

诗歌鉴赏
                                                                                             宿桐庐江寄广陵旧游①
                                                                                                        孟浩然
                                                                                          山暝听猿愁，沧江急夜流。
                                                                                          风鸣两岸叶，月照一孤舟。
                                                                                          建德②非吾土，维扬③忆旧游。
                                                                                          还将两行泪，遥寄海西头④。
注释：①旧游：指故交。②建德：今浙江省建德县一带。③维扬：即扬州。④海西头：指扬州。

中国人口问题的主要矛盾是（   ）