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to be mixed in with; to blend with
「混じる」 has another reading with different meanings.
年を取って白髪が黒髪に混じってきている。
Gray hair is mixed in with black hair.
外国人が観客に混じっていた。
Foreigners were mixed in with the audience.
検査の結果、不純物が水に混じっている。
Impurities are mixed in the water.