Multiple choice questions. You MUST include the calculations. [Each question has 2 marks] 7. A Brillouin light scattering experiment was carried out in a 180-degree scattering geometry with 1=660 nm probing light. The measured Brillouin frequency shift for an unknown material was found to be f=02x= 25 GHz. In a separate measurement using an Abbe refractometer, the refractive index for the same material was measured to be n=1.47. Based on the parameters provided, find the correct speed of sound in an unknown material by choosing one of the answers below: A. 5.65 m/S B. 5.34 km/s C. 534 m/S D. 5.61 km/s