In each of the following sentences is necessity of some action is stated.
Use "to be" instead of "must/have to" to show that the action is not only necessary but also expected or planned.
1) I must buy a present for her birthday
2) We had to take the letters to the post-office
3) I have to make a report at the conference
4) They mush show us how to organise the work
5) She had to take this group pf children round the oicture gallery
6) We had to start early
7) I must do the shopping today
8) I must explain it all to you