读下面的“等高线地形图”，完成下列问题。

魏晋南北朝以来，全国经济重心出现南移的趋势，到___________时，南方已成为全国经济的重心（　　）

读下面的古诗，完成题目。

                                                                                                                                               望岳
                                                                                                                               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。