A. Her book report is due Thursday she hasn't read the book yet.
is the run-on sentence.
This is because a run-on sentence is a sentence in which two complete thoughts are trying to be conveyed, without proper use of punctuation and grammar. Â
In this case, "Her book report is due Thursday" and "She hasn't read the book yet", should probably be two separate sentences. Â Or, they could be linked with a comma, as seen in the sentence "Her book report is due Thursday, but she hasn't read the book yet."
Hope this helps!