We warned them, but to no effect.

我们曾告诫过他们，但没起任何作用。

《牛津词典》

Their instincts warned them something was amiss.

他们的直觉警告他们某些地方不对头。

《柯林斯英汉双解大词典》

I've warned them to keep their mouths shut about this.

我警告他们对此事要守口如瓶。

《牛津词典》

She also warned them about the risk of sharing personal information.

VOA: special.2009.02.18

"I warned them that there isn't too much ambiguity.

VOA: standard.2009.10.15

Still,law enforcement officials have long warned about the dangers of young people being identified by adults wishing to harm them.

VOA: special.2009.02.03

He also warned them against equalising charges upwards by raising the price of local transfers.

ECONOMIST: Borders and barriers

Addressing French troops at Timbuktu's airport afterwards, President Hollande warned them that that the mission was still dangerous.

BBC: Mali conflict: Timbuktu hails French President Hollande

They then began to ship heavier, and, as the engineers had warned them, the tracks indeed broke down.

FORBES: Obama Can Make His Own Reality, But Laws of the Universe Won't Necessarily Adhere