Heat water using the sun during the day, and use it during the cold night.
Use a solar panel to charge batteries during the day, and use the power at night.
A is the ans for this question
It's basically a wave that moves back and forth at regular speed through matter. because of that it transfers energy through a medium (matter). however the movement of the wave is limited because of this but it can still move over long distances. so because of this these types of waves don't move far from their original point or Equilibrium position. in short think of throwing a pebble into water and seeing the little ripples from it, that's a mechanical wave.
C is the answer because amplitude is need for wave 2 to be bigger than wave 1
