等比数列{a_n}的前n项和为S_n，已知S₁，2S₂，3S₃成等差数列，则{a_n}的公比为____ 

                                                                                                                  甲

                                                                                                           乡  愁（节选）
                                       后来啊/乡愁是一方矮矮的坟墓/我在外头/母亲在里头/而现在/乡愁是一湾浅浅的海峡我在这头/大陆在那头/
                                                                                                                    乙

                                                                                                            天净沙· 秋思
                                                                  枯藤老树昏鸦，小桥流水人家，古道西风瘦马。夕阳西下，断肠人有天涯。