What is the meaning of genetics

The scientific study of heridity is called genetics.

hope this will make u understand...

20 is 3. 

This is because the first two would not make sense and the last one also does not make sense. On top of that, sound cannot travel through a vacuum which is demonstrated as in space nothing is heard.

21 is 2 kinetic.

This is because the skier originally starts off with potential energy but as speed increases, the skier going downhill, it turns into more kinetic instead of potential.

Hope this helps!