Ответ:
1. I think he knows the truth.
2. They say that he is a student.
3. They say that he was a student.
4. It turned out that he was a student.
5. Announced that the epidemic is over.
6. Reported that all the shops opened.
7. they expect that their studies will end in June.
8. it is known that German is the most expressive language.
9. Russian is considered to be one of the most difficult languages.
10. assume that every student knows English.
11. I think that he is the richest man in the world.
12. a diamond is considered to be the hardest gemstone. ( gem –
precious stone).
13. Expect that this play will be a success. ( play – play).
14. I happen To know this person. ( use the verb happen).
15. it seems that he knows this song by heart.