Question

Which is a run-on sentence?

A.
Her piano lesson starts at 4 o'clock, and she's going to be late.

B.
Her cookies are delicious, so she entered them in the county fair.

C.
Her closet is full of clothes, yet she says she has nothing to wear.

D.
Her book report is due Thursday she hasn't read the book yet.

Answer 1

D. is a run on sentence. All of the other sentences have conjunctions where they need to be, however D. does not. D should have either and or but.
Hope this is helpful

Answer 2

A run-on sentence is a sentence that doesn't have appropriate punctuation. Having this in mind, the correct answer is D. Her book report is due Thursday she hasn't read the book yet.
There should be a comma after Thursday, or some kind of a conjunction.