Nah, I've had my share of casual sex and the guy doesn't need to be a model. Looks help, attraction (not entirely looks based) even more, but making you feel at ease with him and like you're on the same page is vital. Sometimes someone is hot and they open their mouth and you lose all attraction. Other times, someone is so so and all of the sudden you two click and the chemistry between you is high.
Also, studies show women are highly impacted be scent - especially if they aren't on the pill. It helps us realize good genetic matches.
I answered C. A wouldn't be right because it takes more than just looks to have good sex. B isn't right either because you don't need to share "common interests" or things like that. You just need to get along and have good sex together.
You don't need to be attractive or have a good personality for me to have casual sex with you. I only care about that for relationships. Although I've only had casual sex twice, so maybe I am not the best person to ask for that. Neither had to do with looks. One was a good friend and we both really wanted sex and we were both single. Another was a bar thing. That was way back in my early 20's though for both. Now I just have sex in relationships.