Refraction of light — practice question

A ray of light travels from air into a glass block, as shown. Which expression gives the refractive index of the glass?

• A$\dfrac{\sin w}{\sin y}$
• B$\dfrac{\sin w}{\sin z}$
• C$\dfrac{\sin y}{\sin w}$
• D$\dfrac{\sin z}{\sin x}$