Open your books at page …Twenty one.
-
the
a
an
Don't take any…. books from the case.
-
the
a
an

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вопрос

I see that you are struggling with the indefinite articles "a" and "an." Let me explain:

"A" is used before words that begin with a consonant sound."An" is used before words that begin with a vowel sound.

For example:

"A book" (b is a consonant sound)"An apple" (a is a vowel sound)

So in the sentence "Don't take any… books from the case," the correct choice would be "any." So it should read:
"Don't take any books from the case."