Which law states, "the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward

Which law states, "the effect produced by a moving source of waves in

1.	Which law states, "the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward
A.	Stefan's law
B.	Doppler's effect
C.	Kirchhoff's law
D.	Newton's law of cooling
Answer» C. Kirchhoff's law