What is it?
It's an arm. (or This is a...)
What is it?
It's a hand. (or This is a...)
What is it?
It's a foot. (or This is a...)
What is it?
It's a knee. (or This is a...)
What is it?
It's a leg. (or This is a...)
What is it?
It's a head. (or This is a...)
What are they?
They're toes. (or These are ...)
What are they?
They're fingers. (or These are ...)