19. As far as we know, it took him more than a year to write the book.
20. It has been proved that every substance, no matter what it is, is made up of atoms.
21. It has been decided that we are going to build a railway whose base must be completed within this year.
22. It is obvious (evident) that the success of the innovation depends on our concerted efforts.
23. To be frank, whether you like it or not, you have no other choice.
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