Consider a rectangular coordinate system (x, y, z) with unit vectors ax, ay and az. A plane wave travelling in the region z ≥ 0 with electric field vector E = 10cos(2 × 108t + βz)ay is incident normally on the plane at z = 0, where β is the phase constant. The region z ≥ 0 is in the free space and the region z < 0 is filled with a lossless medium (permittivity ε = ε0, permeability µ = 4µ0, where ε0 = 8.85 × 1012 F/m and µ0 = 4π × 10-7 H/m). The value of the reflection coefficient is

Answer: Option B