Answer: C - it's a sentence fragment because it doesn't have a subject.
Explanation:
While you'll see this type of sentence in TV shows and normal speech, technically it's incomplete. Who is telling us all what really happened?
It should be connected with a sentence with a subject, like- "It's time she started talking- to tell us all what really happened."
Or- "It's time she told us all what really happened."
It's got to involve a pronoun somehow. Hope this helped