1. Yesterday I updated my facebook after I.... my homework
2. Tomorrow I will update my facebook after I .... my homework
3. We tried the product before we ..... to buy it
4. We should try the product before we .... to buy it
5. When I .... there, the headmasterhad already left.
6. while I was walking home, I ... an old friend
7. By the time I leave this city, I..... here for two years