六小时后她仍未回家，所以他们报了警。

Six hours later she still wasn't home so they ___alerted the police.

卡尔·马克思警示我们所有人，工作可能导致异化。

Karl Marx ___alerted us all to the fact that work can cause alienation.

气压的骤降向船长警示了即将来临的风暴。

The sudden drop in barometric pressure ___alerted the captain to the approaching storm.