Final answer:
The appropriate article to fill in the blank is O. unas.
Step-by-step explanation:
The appropriate article to fill in the blank is unas.
The sentence 'Hay un libro y______________papeles en el escritorio.' translates to 'There is a book and ______________ papers on the desk.'
Since the noun 'papeles' is plural, the correct article to use is 'unas.'
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