What is testable explanation for an or event or phenomena

Which is not a source of noise pollution? a)airplanes b)acid rain c)machines d)cars

Based on the concept of the wave-like nature of light, huygens' theory of light postulates that the more light was "bent" by a substance the slower it would move while traversing across that substance. a) deflection b) interference c) refraction d) resonance

What’s #16 asking me and how do i solve it?