Which sentence is a run-on sentence?

The greatest gift the sumerians gave the world was the invention of writing. the sumerians were wealthy people. they needed some way to keep track of what they owned. they began drawing pictures. they used a reed as a pen. they drew on soft pieces of clay. the soft clay was then dried in the sun. the tablet became a permanent record. later, the sumerian drawings changed into wedge-shaped symbols. this kind of writing is called cuneiform. by putting symbols together, the sumerians could write entire sentences.

The implicit details in this excerpt best support the conclusion that mrs. long feels angry about having to ask to borrow books. the speaker asks for books that were often difficult to find. the speaker appreciates the librarian's efforts to get her books. young children are not allowed to borrow books on their own.

You evaluated the effectiveness of tan's structure in supporting her purpose.