"It is national book week."
Translation:C'est la semaine nationale du livre.
Can somebody please explain why "du" is correct and "de" cannot be used?
If you said "la semaine nationale de livre", "livre" would have no article (and it needs one).
Du = de + le
"C'est la semaine du livre national" was rejected. I gave some thoughts on this. It is a national week, rather than a book week.