1. I met / was meeting the professor while I did

1. I met the professor while I was doing the shopping.
2. I was looking through the magazines when I heard someone call my name.
3. When I saw him he was wearing the same old black hat.
4. We decided to have a cup of tea together.
5. When I finished typing my article I went home.

We use Past Indefinite and Past Continuous. Past Indefinite is formed with the help of the suffix ed for regular verb. We use the second form of irregular verbs in Past Indefinite.

Past Continuous is formed with the help of the auxiliary verb to be (am, is, are). We add the suffix ing to verb.