The correct answer is: desertification.
Desertification is a process in which a land which was not a desert before, becomes one. This process can include drying out- through for example loss of water source, such as river diversion- and the loss of vegetation.
The one that makes the most sense to me, would have to be B. A would not be a benefit at all. While C doesn't necessarily makes sense as the device is only designed to capture energy from ocean waves. And D doesn't make sense to me in general.
Distance between corresponding points 2 consecutive waves