They make threats but back down at the first sniff of trouble.
他们起先气势汹汹，但一看情形不妙立刻软了下来。
I'll take you back down to the valley.
我会带你返回下面的山谷里。
His determination and refusal to back down had won the day
他的坚定和拒不退让使他赢得了胜利。
It's too late to back down now
现在打退堂鼓已经太晚了。
I drove back down the highway at normal speed
我以正常车速沿公路返回。