На passive. нужно написать personal или impersonal форму каждого предложения, в зависимости от самого предложения
1. they are expected to arrive in the next few minutes.
it
2. it has been reported that they have found the missing documents.
the missing documents
3. it is thought that the students are planning a surprise for theit teacher.
the students
4. he is known to be working for local council.
it