Complete each sentence so that it contains might, might not, must,

Complete each sentence so that it contains might, might not, must, mustnt, cant or can. More than one answer may be possible.
1. Were not sure but we _________ go to Prague for Christmas this year.
2. Bill cooked the lunch, so you _________ expect anything special!
3. You really ________ start spending more time on your work.
4. Thats really stupid idea! You _______-be serious, surely!
5. You ________ realize it, but this is very important to me.
6. Tell Mike he _________ take my book if he needs it.