[单选题]
The angle of incidenc8tffx9i+ 36fa h0(qul qbj3ox yoy3 5( l-g4pb+n jekv8:i j,i fcm j)6c5lhtue
A. must equal the angle of refraction.
B. is always less than the angle of refraction.
C. is always greater than the angle of refraction.
D. may be greater than, less than, or equal to the angle of refraction.