a rap on the knuckles的用法和样例：
- He got a rap on the knuckles for his bad work.
- He got a rap on the knuckle for his bad work.
- The bank clerk got a rap on the knuckles for his carelessness.
- The child's father gave a rap on the knuckles as a physical punishment.
- He got a rap on the knuckles from the teacher's stick because he was holding his pen in a wrong way.
- The result was that he lost his broker's commission and in all probability got a rap on the knuckles from his boss!