Use the right form of the Infinitive
1 You hadbetter (come) at once.
2 They seem ( work) in the library now/
3 This telegram must (send) immediately
4 Many passengers were known (save)

1 You had better come at once.
2 They seem to be working in the library now.
3 This telegram must be sent immediately
4 Many passengers were known to have been saved.