In the Figure,in the Investigation of a New Type of Optical

In the figure,in the investigation of a new type of optical fiber (index of refraction n = 1.26) ,a laser beam is incident on the flat end of a straight fiber in air.What is the maximum angle of incidence θ₁ if the beam is not to escape from the fiber?

A) 50.0°
B) 46.9°
C) 43.8°
D) 40.7°
E) 37.6°