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。