Here's a problem to solve: Wind is becoming more common as a source of energy. Wind farms require large open spaces for the wind turbines. A negative consequence of this technology is wind turbines

Among the 4 following options, which is the correct answer?

- A: are an inexpensive source of energy.
 
- B: cause little pollution to the environment.
 
- C: may hurt the flying animals in the area.
 
- D: are a renewable source of energy.
 