They defied him to jump off the bridge.

跳下桥去。

Are you stark raving mad, jumping off a moving train?

你疯了吗？居然从行驶的火车上跳下来。

They were very foolhardy to jump off the bus while it was still moving.

"公共汽车还未停就跳下了车,真是太莽撞了。"