a pack of playing cards的用法和样例：
- Can you lend us a pack of playing cards?
- Excuse me. Could I have a pack of playing cards, please?
- A pack of playing cards;
- There's a tank of frog spawn, a pack of self-shuffling playing cards, and other wonders here.
- Two cards are chosen at random, one by one, from a pack of 52 playing cards without replacement.