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.
In this case, "Her book report is due Thursday" and "She hasn't read the book yet", should probably be two separate sentences. 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!
