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たまたま， 偶々， 偶偶， 偶， 適
1. by chance, by accident, accidentally, happen to (be, do), unexpectedly, casually
2. occasionally, once in a while, now and then
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
