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乗り換え， 乗換， 乗換え， 乗り替え， のりかえ
1. transfer (trains, buses, etc.), change, connection
2. switch (to another ideology, party, system, method, etc.), change, conversion
3. switching (stock)
4. chromosomal crossover, crossing over
tbd
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必要， 必用， ひつよう
1. necessary, needed, essential, indispensable
2. necessity, need, requirement
必要的，必需的，必不可少的，不可缺少的；必要性，需要，要求
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
