posted by me .
A researcher designs an experiment to determine if German Shepherds prefer pet doors that opens from the side or from the top. He installs two pet doors side-by-side in the same wall. The pet door that opens from the top is designed for pets up to 15 pounds. The one that opens from the side is designed for animals up to 220 pounds. The German Shepherds in his study used the-side opening pet door. The researcher determine that German Shepherds prefer pet doors that open from the side. This situation is an example of: