Unlike Carol's interpretation, (A) arguably frames Ming's remarks the right way, treating healthiness as a spectrum. That's precisely the opposite of Carol's understanding, which focuses on whether trans fats make a cookie healthy or not.

From Carol's objection that "desserts aren't healthy!" we can infer that, in Carol's mind, Ming is arguing that desserts are healthy (once you remove trans fats). That's probably not what Ming means, but this question is about Carol's interpretation of Ming's remarks.

For (C) to be right, Carol's point must be "There are more options besides healthy and unhealthy, you know!"

But it's Carol who arguably thinks of things in stark healthy or unhealthy terms.

Carol acknowledges that many of the cookies no longer have trans fat. She doesn’t mention any foods with trans fat.

Neither speaker says anything about what consumers should or shouldn’t buy.