After the tree fell onto the road，they put a warning sign in front of it.
树倒在路上之后他们在前面放了一张警告牌。

The man yelled a warning to the boys on ice.

那个人大声向冰上的男孩们警告。

This is a warning sign for an imminent eruption.

这就是火山临近爆发前的一个警示信号。

I flashed a warning glance at them.

我向他们投去警告性的一瞥。

※The overturned cart ahead is a warning to the carts behind. 前车之覆，后车之鉴。