Chinese languages

I'm working on a chinese language learning website and am interested in borrowing some content from one or more established source. I have heard that the vocabulary lists from NPCR, PCR, and Integrated chinese are public domain. I have also seen digitized versions of some of these texts available online. My question is simple.

Is the text of any of these popular chinese textbooks free for use or are they all copyrighted?

Please accompany any answer with some evidence, a link, or anything that I can actually use to confirm whether or not any of these texts are available for use. Thanks.


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