A ducks quack is made by a duck makeing a sound that reflects around it's beak, making a quack.
The platypus is not like a bird. It is an egg-laying mammal. The eggs it lays are soft-shelled and leathery.
OMFG it's a duck!!
Of course. Anything with a beak and feathers are birds, even if they can't fly or is super large.
Yes, a duck can quack.