A Light Wave Traveling at Speed V₁ in Medium 1

A light wave traveling at speed v₁ in medium 1 passes into medium 2 where its speed is v₂. By which of the following equations is the frequency f₁ of the wave in medium 1 related to its frequency f₂ in medium 2? θ₁ and θ₂ are the angles of incidence and refraction.)

A) f₁ sin θ₁ = f₂ sin θ₂
B) f₁v₂ = f₂v₁
C) f₁ = f₂
D) f₁v₁ = f₂v₂
E) f₁ sin θ₂ = f₂ sin θ₁