19. D 20. Sorry don’t know but if I had to guess it would be B 21. A because fluorine has a higher electronegativity 22. D 23. B 24. Again don’t really know but I would guess D 25. A
Why: A - this is natural B - water is natural D - this is also natural C- this is right because when we breathe out we produce more carbon dioxide then we breathed in.
