To conduct an appropriately randomized experiment, it's important to have a population that is broad enough to ensure the results are more generalizable and not overly specific to one subgroup, while still being relevant to the study's goal.
Considering the options:
A. Population #1: dogs in California - This option provides a diverse range of breeds and diets, allowing for a more randomized selection of dogs from different backgrounds.
B. Population #2: golden retrievers in Omaha, Nebraska - This option is very specific (only golden retrievers in one city), which limits the ability to generalize results. It may not effectively represent how diet affects activity levels across different breeds and environments.
C. Population #3: poodles in the United States - Similar to Option B, this is also quite specific (only poodles), and while it covers a broader geographical area, it still limits the diversity in breeds.
Given the goal of an appropriately randomized experiment, Population #1: dogs in California is the best choice, as it provides a larger and more diverse sample of dogs that can help in understanding the effects of diet on activity levels more comprehensively.