基差来源是什么？
基差越小，管理风险的成本越低，效率越高。[{'character': '基', 'pinyin': 'ji1', 'highest pitch': 10.24, 'lowest pitch': 9.79, 'duration': 0.2, 'prosody hierarchy': 'null'}, {'character': '差', 'pinyin': 'cha1', 'highest pitch': 10.73, 'lowest pitch': 9.79, 'duration': 0.26, 'prosody hierarchy': '#1'}, {'character': '越', 'pinyin': 've4', 'highest pitch': 11.01, 'lowest pitch': 9.22, 'duration': 0.2, 'prosody hierarchy': 'null'}, {'character': '小', 'pinyin': 'xiao3', 'highest pitch': 9.22, 'lowest pitch': 4.05, 'duration': 0.3, 'prosody hierarchy': '#3'}, {'pinyin': 'sp1', 'highest pitch': 0.0, 'lowest pitch': 0.0, 'duration': 0.12}, {'character': '管', 'pinyin': 'guan2', 'highest pitch': 8.0, 'lowest pitch': 6.3, 'duration': 0.19, 'prosody hierarchy': 'null'}, {'character': '理', 'pinyin': 'li3', 'highest pitch': 8.07, 'lowest pitch': 6.07, 'duration': 0.15, 'prosody hierarchy': '#1'}, {'character': '风', 'pinyin': 'feng1', 'highest pitch': 8.78, 'lowest pitch': 6.08, 'duration': 0.2, 'prosody hierarchy': 'null'}, {'character': '险', 'pinyin': 'xian3', 'highest pitch': 8.54, 'lowest pitch': 4.61, 'duration': 0.15, 'prosody hierarchy': 'null'}, {'character': '的', 'pinyin': 'de5', 'highest pitch': 5.57, 'lowest pitch': 4.27, 'duration': 0.1, 'prosody hierarchy': '#1'}, {'character': '成', 'pinyin': 'cheng2', 'highest pitch': 8.66, 'lowest pitch': 5.57, 'duration': 0.25, 'prosody hierarchy': 'null'}, {'character': '本', 'pinyin': 'ben3', 'highest pitch': 8.96, 'lowest pitch': 6.0, 'duration': 0.16, 'prosody hierarchy': '#1'}, {'character': '越', 'pinyin': 've4', 'highest pitch': 11.01, 'lowest pitch': 6.05, 'duration': 0.2, 'prosody hierarchy': 'null'}, {'character': '低', 'pinyin': 'di1', 'highest pitch': 9.54, 'lowest pitch': 8.7, 'duration': 0.26, 'prosody hierarchy': '#3'}, {'pinyin': 'sp1', 'highest pitch': 0.0, 'lowest pitch': 0.0, 'duration': 0.18}, {'character': '效', 'pinyin': 'xiao4', 'highest pitch': 10.45, 'lowest pitch': 8.78, 'duration': 0.24, 'prosody hierarchy': 'null'}, {'character': '率', 'pinyin': 'lv4', 'highest pitch': 8.9, 'lowest pitch': 8.14, 'duration': 0.13, 'prosody hierarchy': '#1'}, {'character': '越', 'pinyin': 've4', 'highest pitch': 11.01, 'lowest pitch': 6.96, 'duration': 0.2, 'prosody hierarchy': 'null'}, {'character': '高', 'pinyin': 'gao1', 'highest pitch': 10.14, 'lowest pitch': 8.93, 'duration': 0.3, 'prosody hierarchy': '#4'}]