A pocket knife的用法和样例：
- My brother bought me a pocket knife yesterday.
- A pocket knife is a handy tool for any camper or hiker.
- No, I think it must have been the cheap pocket knife that the Beyer's had given me in Laramie that first Christmas.They said every man in the West had to have a pocket knife.
- I find a surplus store and buy a pocket calculator.
- He always carries a pocket dictionary with him.