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今日， きょう， こんにち， こんち， こんじつ
1. today, this day
2. these days, recently, nowadays
今天
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希薄， 稀薄， きはく
1. thin (air), weak (liquid), dilute, sparse (population), rarefied
2. lacking (enthusiasm, consideration, substance, etc.), insubstantial, deficient, tenuous (link)
tbd
は
1. indicates sentence topic
2. indicates contrast with another option (stated or unstated)
3. adds emphasis
指示句子的主题；表示与另一选项（无论是否明确提及）形成对比；表示强调
