The answer to this is A. this is because, refraction with a light or sound wave changing its direction involve propagation,(in which propagation is the change in direction of a light or sound wave)
Increase .... decrease .... presumably it's the "best shape" for a body which has been formed by the gravitational force
The correct option is B.
Resonance is said to occur when one object which is vibrating at the same natural frequency of a second object forces the second object into vibrational motion. When resonance is achieved a big loud voice is usually heard. Resonance generally requires three conditions to occur:
1. An object that has a natural frequency.
2. A force that is functioning at the same frequency as the natural frequency.
3. Prevention of energy loss.
