The third choices does not contain a run on sentence due to there being 2 sentences in the answer choice.
D. His isolation from humanity is the most likely reason that a reader of Frankenstein would find the creature somewhat sympathetic.
It is a rejected creature - everybody is afraid of him and hates him. This is the reason why a reader will sympathize with the lonely monster who didn't even ask to be created.
I would say that this sentence contains examples of colloquialism.
Colloquialism is <span>a word or phrase that is not formal or literary and is used in ordinary or familiar conversation.</span>
Becuase the kids in the schoold multiplied and ppl realised it was becoming harder for teachers to teach so many different school levels at once
If anything, it made it a bit more frightening... It gave the reader access to his insane mind.