Answer:
The correct answer is option A) "Repeat the experiment by removing the patch completely".
Step-by-step explanation:
In this example, researchers believe that European robins have a territorial defense pattern where they attack anything similar to orange feathers, including an orange patch. In order to establish if the color initiated defense response is real it is necessary to repeat the experiment by removing the patch completely. If the European robins do not longer attack, then the researchers can conclude that the color initiated defense response is real.