No, this is not a run-on sentence
Hypothetical in my opinion because their not meaning it literally
The correct answer is C. She came by to pick up her purse and cell phone, which she had left in my apartment.
Explanation:
In grammar, concrete nouns are words that describe specific and tangible entities such as objects, places, people, etc. In the case of the sentence presented the word "things" is not a concrete noun as this concept is abstract and too general, this also applies to terms such as stuff or junk.
On the opposite, the words "purse" and "cellphone" are concrete nouns because these refer to tangible and concrete or specific objects. In this context, if the focus is concrete nouns the best revision is option C because this replaces appropriately the abstract noun "things" by two concrete nouns.
