Answer:
Hello~
llamalover here!
The dog is wagging its tail.
Step-by-step explanation:
it's = it is. So the dog wags it is tail does not work.
The dog is wagging its tale. tale means like a fairy tale.
The dog is wags its tail. it doesn't sound right. you don't say The dog is wags its tail. you would say The dog is wagging its tail.
Hope this helps!