Hi Desparatenconfused!
In the stimulus, we have the following reasoning:
Mattress @ Southgate Mall Mattress Madness 20 percent off
That is, if it is a mattress being sold at Southgate Mall, then it is being sold at Mattress Madness, in which case it is 20% off. We can infer that if it is a Mattress being sold at Southgate Mall, then it is 20% off.
Answer choice (C) parallels this reasoning:
Food @ Diane's apartment Refrigerator Purchased within past week
That is, if something is food within Diane's apartment, then it is in the refrigerator, in which case it was purchased within the past week. We can infer that if it is food within Diane's apartment, then it was purchased within the past week. This has the same structure as the stimulus.
Answer choice (D) would be diagrammed as follows:
Food @ Diane's apartment Refrigerator Purchased within past week
So the structure would be identical. However, the problem is the conclusion reached in (D): "Therefore, all the food she purchased within the past week is in her apartment." This doesn't necessarily follow from the diagram. Based on the diagram, we know that if it's food in her apartment, then it was purchased within the past week. But it's possible that she also purchased food in the past week that isn't in her apartment (e.g., perhaps she went out to eat).