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to be careful; to pay attention; to take care
夜道を歩くときは周囲に気をつけるようにしている。
I try to be aware of my surroundings when walking at night.
食べ過ぎに気をつけないと体重が増えてしまう。
If you don't watch out for overeating, you'll gain weight.
段差があるので足元に気をつけてお進みください。
Please watch your step as there is a difference in level.