Parrots can develop cognitive issues as they get older. This may compromise their memory, ability to learn, awareness, sight, and hearing. A researcher wishes to conduct a study to find which of two medicines, Medicine A or Medicine B, is more effective in improving cognitive health. A total of 150 parrots that are at least 12 years old will be randomly selected from sanctuaries around the United States. The researcher will get consent from all owners, treat the parrots for 1 year, and evaluate changes in cognitive health.

Part A: How would the study benefit from adding a control group?

Part B: What is the best way to randomly place the parrots into the Medicine A, Medicine B, and control groups?

Part C: The researcher wants to use a blocking variable to place the parrots into groups instead of doing it randomly. He decides to block either by breed or sanctuary. Explain which would be the best blocking method.