根据nltk 源码进行标签映射
'CC': 'Coordinating conjunction', 'PRP$': 'Possessive pronoun',
'CD': 'Cardinal number', 'RB': 'Adverb',
'DT': 'Determiner', 'RBR': 'Adverb, comparative',
'EX': 'Existential there', 'RBS': 'Adverb, superlative',
'FW': 'Foreign word', 'RP': 'Particle',
'JJ': 'Adjective', 'TO': 'to',
'JJR': 'Adjective, comparative', 'UH': 'Interjection',
'JJS': 'Adjective, superlative', 'VB': 'Verb, base form',
'LS': 'List item marker', 'VBD': 'Verb, past tense',
'MD': 'Modal', 'NNS': 'Noun, plural',
'NN': 'Noun, singular or masps', 'VBN': 'Verb, past participle',
'VBZ': 'Verb,3rd ps. sing. present', 'NNP': 'Proper noun, singular',
'NNPS': 'Proper noun plural', 'WDT': 'wh-determiner',
'PDT': 'Predeterminer', 'WP': 'wh-pronoun',
'POS': 'Possessive ending', 'WP$': 'Possessive wh-pronoun',
'PRP': 'Personal pronoun', 'WRB': 'wh-adverb',
'(': 'open parenthesis', ')': 'close parenthesis',
'``': 'open quote', ',': 'comma',
"''": 'close quote', '.': 'period',
'#': 'pound sign (currency marker)',
'$': 'dollar sign (currency marker)',
'IN': 'Preposition/subord. conjunction',
'SYM': 'Symbol (mathematical or scientific)',
'VBG': 'Verb, gerund/present participle',
'VBP': 'Verb, non-3rd ps. sing. present',
':': 'colon',