The answer is A. a light wave
C and D both need water as a medium and sound needs air to vibrate in order to travel. light, on the other hand, does not need a medium
C. Permafrost
Permafrost is the layer beneath the "active layer". The active layer consists of soil that freezes and thaws every year. However, the requirement for permafrost is that it be frozen for two or more years consecutively. This is why permafrost exists in cold environments such as tundras.
Our sun<span> is the only </span>source of energy<span> that does propels of the </span>water cycle<span>. It's heat, or hot substance causes the surface evaporation that begins cycles.</span><span> The </span>water cycle<span> begins with the </span>sun, <span> and wind causing </span>water<span> to evaporate. The </span>water<span> is only carried high, not low above the earth's surface on rising currents of air.
Hope that this helps you! =)</span>
