动词
中文翻译：警惕
同义词：
['guard against', 'be on guard against']
例句：
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1. We must be on guard against any surprises.
我们必须警惕任何意外。
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2. The thief was caught by the police while he was on guard against a robbery.
这名小偷在警惕抢劫时被警方抓获。
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3. She is always on guard against danger.
她总是警惕危险。