before one can say Jack knife

• 马上；立即

before one can say Jack knife的用法和样例：

例句

1. They cannot readily agree to it.
   他们不能对此马上作出应诺。
2. I can't say offhand exactly how much.
   我不能立即告诉您多少钱。
3. Two of these can be taken off the list immediately.
   其中两个能立即从名单上去掉。