a quack doctor的用法和样例：
- He is a quack doctor.
- The King cursed the courtiers and clapped them quickly into clink for taking pres criptions from a quack doctor.
- That doctor is just a quack, he should be reported.
- Next door there lived a quack doctor from his village who admired Fang's reputation and found time off between killing people to drop by occasionally for a chat.
- Don't be taken in he's just a quack.