Final answer:
The word that best completes the sentence is 'concerned'. It means that the paper lacked a clear connection or relevance to the book it was supposed to be about.
Step-by-step explanation:
The word that best completes the sentence is concerned. The sentence is: My teacher said that my paper didn't seem to be concerned with the book upon which it was supposed to be written. In this context, 'concerned' means that the paper lacked a clear connection or relevance to the book it was supposed to be about.
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