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.