What is the source of wave motion?

I would think it would be an object such as a rock dropping in the water. How this translates into an answer, however, I'm not sure. :-)

After reading the answer in the website, I still wan't sure of the answer because it gives a multiple choice answer and you are supposed to pick the correct one. I reincluded the question and then gave my answer. is this correct?

What is the source of wave motion?

The source of wave motion is the transfer of energy by a vibrating or moving object such as an engine, vibrating air molecules, or a rock thrown into a pond.