'Declare', 'declare as', or 'declared as a'

[AlbaRubio]

Hello everyone. I have been struggling to make a right use of this verb. Could you tell me when to use each form. For example for the next sentence, how would it be:

-These islands, declared as National Park, are a paradise for nature lovers and offer some of the best beaches in Spain

-These islands, declared National Park, are a paradise for nature lovers and offer some of the best beaches in Spain

- These islands, declared as a National Park, are a paradise for nature lovers and offer some of the best beaches in Spain

If you can give a short explanation of the use of each of them, I would really appreciate it. Cheers!

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[5jj]

These islands, declared a National Park, are a paradise for nature lovers and offer some of the best beaches in Spain.

Declare in this sense does not need as. National Park does need an indefinte aricticle.