1. As a verb (make the sound of a duck):
* The duck quacked loudly as it swam in the pond.
* The children giggled as they imitated the quacking of the ducks.
* The sound of the quacking filled the air, creating a peaceful atmosphere.
2. As a noun (the sound of a duck):
* The quack of the duck woke me up early this morning.
* The quack of the ducklings echoed through the park.
* The farmer recognized the quack of his prize-winning duck.
3. As a noun (a person who practices medicine without proper qualifications):
* He was accused of being a quack and treating patients without a license.
* Don't trust that quack with your health; he's just trying to make a quick buck.
* The quack promised to cure all your ailments with his miracle potion.
4. As an adjective (informal, disapproving):
* That's a quack idea; it's not going to work.
* Don't listen to that quack doctor; he doesn't know what he's talking about.
* The quack salesman tried to convince me to buy his useless product.
5. As an interjection (imitate the sound of a duck):
* Quack! (To imitate a duck)
* Quack, quack, quack! (To express excitement or joy)
Remember that using "quack" as a noun or adjective referring to an unqualified doctor can be offensive. Use it carefully and consider the context.