Words to Miyo
Were you, or weren’t you?
We reviewed can and went on to the past tense (Could you swim when you were five?).
No problems here, you seem to understand this fine.
Then we worked on the past of be (Where were you at five o’clock? Why weren’t you there?).
Again, you seemed to have no trouble with the grammar point–I guess you know the past tense fairly well.
Don’t forget to consider the situation and context, though, not only the grammar. For example, Miguel and Emma were talking about last night’s party.
Miguel says: “Where were you? Why __ you there?” Were doesn’t fit the situation–if she was there, he wouldn’t need to ask–so it has to be weren’t.