A light beam is traveling from Region I to region IV (refer figure). The refractive indices in Region I, II, III, and IV are `n_(0), n_(0)//2,n_(0)//6 and n_(0)//8` , respectively. The angle of incidence `theta` for which the beam just misses entering Region IV is
A. `sin^(-1)(3/4)`
B. `sin^(-1)(1/8)`
C. `sin^(-1)(1/4)`
D. `sin^(-1)(1/3)`
