[单选题]
94.11: The critical ag*0+rcek6yeyv u n 4f: 7t8oep)+hhkhu9 qv4i f*p0fg*eyyk0 ngle of a material is the angle of incidence for which the angle of refraction 9phof4 et8ype*h7 +0uvki*q h0k )gyfis:
A. $0^{\circ}$
B. $30^{\circ}$
C. $45^{\circ}$
D. $90^{\circ}$
E. $180^{\circ}$
