Leo is testing different types of greenhouse material to determine which type is most effective for growing strawberry bushes. He purchases two different brands of tarps from a local store. Leo applies brand A to an area of the yard that receives full sunlight and brand B to another area of the yard that is in partial shade. He waters both areas daily. At the end of the study, Leo concludes brand A is more effective in growing strawberry bushes. Is Leo's conclusion valid? Explain why or why not.