美国是世界上最大的玉米生产国之一。
去年，中国采购了大量美国玉米。[{'character': '去', 'pinyin': 'qv4', 'highest pitch': 9.99, 'lowest pitch': 9.06, 'duration': 0.23, 'prosody hierarchy': 'null'}, {'character': '年', 'pinyin': 'nian2', 'highest pitch': 9.06, 'lowest pitch': 7.27, 'duration': 0.33, 'prosody hierarchy': '#3'}, {'pinyin': 'sp1', 'highest pitch': 0.0, 'lowest pitch': 0.0, 'duration': 0.03}, {'character': '中', 'pinyin': 'zhong1', 'highest pitch': 10.83, 'lowest pitch': 10.12, 'duration': 0.21, 'prosody hierarchy': 'null'}, {'character': '国', 'pinyin': 'guo2', 'highest pitch': 10.36, 'lowest pitch': 9.66, 'duration': 0.13, 'prosody hierarchy': '#1'}, {'character': '采', 'pinyin': 'cai3', 'highest pitch': 9.66, 'lowest pitch': 5.6, 'duration': 0.23, 'prosody hierarchy': 'null'}, {'character': '购', 'pinyin': 'gou4', 'highest pitch': 8.41, 'lowest pitch': 7.59, 'duration': 0.16, 'prosody hierarchy': 'null'}, {'character': '了', 'pinyin': 'le5', 'highest pitch': 7.59, 'lowest pitch': 6.77, 'duration': 0.16, 'prosody hierarchy': '#1'}, {'character': '大', 'pinyin': 'da4', 'highest pitch': 10.34, 'lowest pitch': 9.08, 'duration': 0.21, 'prosody hierarchy': 'null'}, {'character': '量', 'pinyin': 'liang4', 'highest pitch': 9.08, 'lowest pitch': 7.21, 'duration': 0.24, 'prosody hierarchy': '#1'}, {'character': '美', 'pinyin': 'mei3', 'highest pitch': 7.21, 'lowest pitch': 4.58, 'duration': 0.17, 'prosody hierarchy': 'null'}, {'character': '国', 'pinyin': 'guo2', 'highest pitch': 10.36, 'lowest pitch': 5.95, 'duration': 0.17, 'prosody hierarchy': '#1'}, {'character': '玉', 'pinyin': 'v4', 'highest pitch': 10.31, 'lowest pitch': 7.3, 'duration': 0.19, 'prosody hierarchy': 'null'}, {'character': '米', 'pinyin': 'mi3', 'highest pitch': 8.85, 'lowest pitch': 1.45, 'duration': 0.34, 'prosody hierarchy': '#4'}]