The correct answer is D. flying over United States cities
That's because drones can be used for anything. They can even be used for spying on someone or assassination. That's why people are scared of others spying on them or of something worse happening.
I had to look for the options and here is my answer:
The description given above describes the theory CONTROL THEORY. In the control theory, there is a tendency that we deviate ourselves. This theory possesses both the inner and the outer controls. This tendency to deviate is also affected by different factors around us.