Mary's never been here before, ________ she?

阅读下面的诗文，回答相关问题。

                                                                                                          《饮酒》
                                                                                                            陶渊明

                                                                                             结庐在人境，而无车马喧。
                                                                                             问君何能尔，心远地自偏。
                                                                                             采菊东篱下，悠然见南山。
                                                                                             山气日夕佳，飞鸟相与还。
                                                                                              此中有真意，欲辩已忘言。

西北地区的主要自然特征（    ）

在宇宙飞船上划燃火柴，火焰会立即熄灭，这是因为（   ）