Gerbils can develop gastrointestinal tract issues as they get older that may cause severe diarrhea and dehydration from the diarrhea. A researcher wishes to conduct a study to find which of two antibiotics, antibiotic a or antibiotic b, is more effective in improving gastrointestinal tract health. A total of 300 gerbils that are at least one year old will be randomly selected from zoos in the state of Florida. The researcher will get consent from all owners, treat the gerbils for 10 months and evaluate changes in gastrointestinal health.

part a: how would the study benefit from adding a control group?
part b: what is the best way to randomly place the gerbils into the antibiotic a, antibiotic b, and control groups?
part c: The researcher wants to use a blocking variable to place gerbils into groups instead of doing it randomly. He decides to block either by breed or zoo. Explain which would be the best blocking method.