Question

1. I have a dog, Lucky. He is cute.
2. I have a dog, Lucky. She is cute.
3. I have a dog, Lucky. It is cute.
[Can we use all the expressions? Which one is commonly used?]

4. I have a dog who is very smart.
5. I have a dog which is very smart.
6. I have a dog that is very smart.
[Which relative pronoun do we have to use?]

Answer 1

When referring to a person or animal you must use who, whom, he, she, etc. We do not refer to them as an it or that.

Answer 2

I disagree with Lee. Only people are referred to as who. Animals are referred to as that or which.