Answer:
C) Their conclusion should be specific to grape juice on that particular fabric.
Step-by-step explanation:
Experimental design should be capable of testing a hypothesis. With Penny and Nikki experiment (with one type of fabric and one type of pigment) can only answer the effectiveness of different stain removers to remove grape juice pigments from the specific fabric that was utilized. If they wanted to test the effectiveness of different stain removers, they should use different pigments and various types of fabrics. Different chemicals (active ingredients in stain removers) can have a different effect on different pigments or on different types of fabrics.