Supply the correct tense / form of the verbs in the blankets

I Supply the correct tense / form of the verbs in the blankets.
1, I'm sure she (understand) ....... if you explained the situation to her
2, The population of vietnam (increase) .......... very fast for the past years 
3, you look very thoughtful . What do you (think)  ...... about ? 
4, She (phone) .........you as soon as she (come) ........back
5, I (wait) ........in school yerd until you come 
6, He can't (go) .............to work without (have) ........... breakfast