How to tell a dog from a dog

pu1. A young dog is called a dog, and a grown-up dog is called a dog

2017-12-27

OK

pu2. Little Dog: Puppy. Adult dog: dog

2017-12-27

OK

pu3. A young dog is called a puppy, just like a young cow is called a calf. There are times when a grown dog is called a dog because it doesn't sound good

2017-12-27

OK