____ 是流行于黄土高原地区的一种民歌形式。

The tie is the ______size.        

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                                                                                                                    村  夜
                                                                                                                   白居易
                                                                                           霜草苍苍虫切切，村南村北行人绝。
                                                                                           独出门前望野田，月明荞麦花如雪。