Topic: Article,

Best Answer Explained in Below-:

In the sentence "I know someone who wrote __ book about," the correct article to fill in the blank is "a." This is because we are referring to a nonspecific or indefinite book. The article "a" is used before singular nouns that start with a consonant sound and indicates that the speaker is not talking about a particular book but any book that fits the description.

If we were to use "the," it would imply that the listener knows which specific book is being referred to, which is not indicated in the context given. On the other hand, "an" would be incorrect here as it is used with singular nouns that begin with a vowel sound, and "book" starts with a consonant sound. Lastly, using no article could create ambiguity, as it would make the sentence sound incomplete or incorrect.

Therefore, the use of "a" effectively conveys that the speaker is discussing any book written by the person they know, making it the appropriate choice in this context.