1. I do my homework.  Christina said she was doing homework.

2. I do my homework every day.  Kristen said that she did her homework every day.

3. Yesterday I did my homework. Kristen said that she did her homework yesterday.

4. I have been doing homework for ten years.  Kristen said that she had been doing homework for ten years.

5. I have never done homework before.  Kristen, she has never done homework before.