这是为什么？
图为首钢职工昨日在料场紧张地抢卸冻煤。[{'character': '图', 'pinyin': 'tu2', 'highest pitch': 10.44, 'lowest pitch': 9.06, 'duration': 0.28, 'prosody hierarchy': 'null'}, {'character': '为', 'pinyin': 'uei2', 'highest pitch': 10.4, 'lowest pitch': 8.92, 'duration': 0.25, 'prosody hierarchy': '#1'}, {'character': '首', 'pinyin': 'shou3', 'highest pitch': 10.17, 'lowest pitch': 5.62, 'duration': 0.22, 'prosody hierarchy': 'null'}, {'character': '钢', 'pinyin': 'gang1', 'highest pitch': 10.34, 'lowest pitch': 5.77, 'duration': 0.21, 'prosody hierarchy': '#1'}, {'character': '职', 'pinyin': 'zhiii2', 'highest pitch': 9.78, 'lowest pitch': 7.41, 'duration': 0.21, 'prosody hierarchy': 'null'}, {'character': '工', 'pinyin': 'gong1', 'highest pitch': 10.0, 'lowest pitch': 7.43, 'duration': 0.24, 'prosody hierarchy': '#2'}, {'pinyin': 'sp1', 'highest pitch': 0.0, 'lowest pitch': 0.0, 'duration': 0.06}, {'character': '昨', 'pinyin': 'zuo2', 'highest pitch': 7.4, 'lowest pitch': 6.77, 'duration': 0.24, 'prosody hierarchy': 'null'}, {'character': '日', 'pinyin': 'riii4', 'highest pitch': 7.88, 'lowest pitch': 6.47, 'duration': 0.22, 'prosody hierarchy': '#1'}, {'character': '在', 'pinyin': 'zai4', 'highest pitch': 8.33, 'lowest pitch': 6.47, 'duration': 0.17, 'prosody hierarchy': '#1'}, {'character': '料', 'pinyin': 'liao4', 'highest pitch': 10.76, 'lowest pitch': 7.21, 'duration': 0.23, 'prosody hierarchy': 'null'}, {'character': '场', 'pinyin': 'chang2', 'highest pitch': 9.12, 'lowest pitch': 6.41, 'duration': 0.28, 'prosody hierarchy': '#1'}, {'character': '紧', 'pinyin': 'jin3', 'highest pitch': 8.5, 'lowest pitch': 4.13, 'duration': 0.22, 'prosody hierarchy': 'null'}, {'character': '张', 'pinyin': 'zhang1', 'highest pitch': 10.25, 'lowest pitch': 4.72, 'duration': 0.2, 'prosody hierarchy': 'null'}, {'character': '地', 'pinyin': 'de5', 'highest pitch': 10.65, 'lowest pitch': 8.75, 'duration': 0.1, 'prosody hierarchy': '#1'}, {'character': '抢', 'pinyin': 'qiang3', 'highest pitch': 8.07, 'lowest pitch': 4.01, 'duration': 0.26, 'prosody hierarchy': 'null'}, {'character': '卸', 'pinyin': 'xie4', 'highest pitch': 9.0, 'lowest pitch': 5.32, 'duration': 0.2, 'prosody hierarchy': '#1'}, {'character': '冻', 'pinyin': 'dong4', 'highest pitch': 9.86, 'lowest pitch': 7.74, 'duration': 0.2, 'prosody hierarchy': 'null'}, {'character': '煤', 'pinyin': 'mei2', 'highest pitch': 7.74, 'lowest pitch': 5.51, 'duration': 0.34, 'prosody hierarchy': '#4'}]