Which sentence is a run-on sentence?

Athe weather was turning cool, meredith knew that fall was on the way.

b."oliver twist" was written by charles dickens; it is about a boy born into a life of poverty and misfortune.

c.walter was bullied in real life, but he was a leader in his imaginary world.

d.i'll be happy if we read more science fiction stories by issac asimov.?