Ineed with questions 20 and 21 and it’s very hard and i’m struggling with it and if you need to see the picture big then click on it and it will be big

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!