Final answer:
The run-on sentence in the provided options is 'a) Some of our belongings were still in the suitcase, the rest of them were scattered.' It lacks proper punctuation or coordinating conjunction between two independent clauses. Adding 'and' or separating them with a period would correct the run-on.
Step-by-step explanation:
The run-on sentence from the options provided is: a) Some of our belongings were still in the suitcase, the rest of them were scattered. This is a run-on because two independent clauses are joined without proper punctuation or coordinating conjunction. To correct this, one could add a coordinating conjunction like 'and', or use a period to separate the clauses into two distinct sentences. Run-on sentences often occur when there is an incorrect use of punctuation, such as a missing period or semicolon, or an absence of a conjunction joining two independent clauses. Recognizing and correcting run-ons is important for clear and effective writing.