Select the most appropriate option to fill in the blank.

She returned the book after she ______ it.

had read

The most appropriate option to fill in the blank is had read.

The sentence is in the past tense, and the verb "to read" is in the past participle form. The past participle form of the verb "to read" is "had read." It is the most appropriate word to use because it accurately describes the action of reading the book before returning it.

The other options are not as appropriate.

• Reads is the present tense form of the verb "to read." It does not make sense in this context, because the sentence is not about the book being read now.
• Read is the simple past tense form of the verb "to read." It does not make sense in this context, because the sentence is about the book being read before it was returned.
• Was read is the passive voice of the verb "to read." It does not make sense in this context, because the sentence is not about the book being read by someone else.