The attack appeared to be unprovoked and it is thought the killer did not know his victim.

此次袭击看似一起无故发生的事件，并且据说凶手并不认识遇害者。

youdao

We recommend that after 3 months of anticoagulant therapy, all patients with unprovoked PE should be evaluated for the risk-benefit ratio of long-term therapy (Grade 1C).

在3个月抗凝治疗后，所有不明诱因的PE患者都需要进行长程治疗风险-效益比评估（1C）。

youdao

All that history would remember would be an unprovoked aggression by Britain on a weak Germany.

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Russia, Syria's most important international ally, said this appeared to be an unprovoked attack on a sovereign nation.

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Would Argentina's unprovoked aggression be resisted or rewarded?

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