In cinema 4d it look like this[34665-in+cinema+4d.png|34665]
and when it is imported to unity it look like this 
[34667-in+unity.png|34667]
help me to understand why?
Select all your objects in Cinema 4D, right click, and click “Connect Objects + Delete”. Save as a new exported model and try it that way (which will let you undo if you save as a new 3D file).
Alternatively, you can press ctrl+A in Cinema 4D, press C, and export as a new 3D file.
I would verify that all of your faces (polys) are aligned. It looks like some some are facing the other way and Unity doesn’t render the back of faces.