student's book, ex. 1, pg. 80
1. had to (obligation, not a regret)
2. couldn't find ( past ability)
3. must have gone (logical deduction)
4. had to work ( an obligation)
5. shouldn't have said (criticism about a past event)
6. needn't have bought (it wasn't necessary to do that action)
7. should have asked (advice) // would have given
8. can't have done (logical conclusion)
9. could have told (criticism) // wouldn't have got up (imagined result)
10. could have been (a possibility that didn't happen)