Answer:
a middle school reader about the mystery of a hidden treasure discovered by a group of teenage boys
Explanation:
According to the given question, Samir, who is an eleventh grader wants to read something complex that will challenge his fluency and vocabulary.
Therefore, the best solution from the list of given options would be to read a middle school story about the mystery of a hidden treasure discovered by a group of teenage boys.
This is because, it challenges his perception and helps him learn new words.