Past Simple or Past Continuous?

[LenkaMM]

Hello,
Should the past simple or past continuous be used in the number 3, please?

While I was (be) in a History class yesterday, something very unusual 1__________(happen). Our teacher 2__________(tell) us about Queen Boudicca and how she 3__________(fight) the Romans, when suddenly I 4__________(hear) a noise behind me.

 

[Tarheel]

Where did you see that?

 

[Skrej]

We need a source of the question before we answer anything. Is this homework?