The police have questioned him thoroughly, and he'll be on his guard.

警察已仔细盘问了他，因此他会保持警惕。

《柯林斯英汉双解大词典》

He thought it best to be on his guard.

他认为他最好还是要警惕。

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He was on his guard, fearful of any pursuit by the gang boss or his men.

他很警惕，害怕被帮派老板和其同僚追杀。

youdao

He said he is now constantly on his guard on a night out.

BBC: Mansfield pub glass attack victim wants plastic cups used

The poll also found that the dispute over Kerry's antiwar activism after the Vietnam War is having more of a negative effect on his candidacy than questions about Bush's National Guard service are having on his electability.

CNN: Bush apparently leads Kerry in pre-debate poll

His personal archive of documents will be packed up and, at 20:00 (19:00 GMT) on Thursday, the Swiss Guard on duty at his Castel Gandolfo residence will be dismissed, to be replaced by Vatican police.

BBC: Pope Benedict XVI recalls joy and 'choppy waters'