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极夜北极光
*be on the alert*heighten one's vigilance
幸福、定格
The flu is absolutely simple, we must heighten our vigilance.
云飞扬了
We should be vigilant
珊珊来了
原用法是对的, of不能删."of + 名词" 很多可以等价于形容词, 做表语, 是正式用语. 比如It is of help. = It is helpful.
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