If when you raise the stage a white line moves from the oute

If, when you raise the stage, a white line moves from the outer edge of a crystal to the inner edge, then __________.
a. The crystal has a higher RI than its surrounding.
b. The crystal has a lower RI than its surrounding.
c. The line is called a refractive dispersal line
d. a and c.
e. b and c.

Solution

since white line or light moved towards the inner edge it means the crystal has higher RI than its surrounding.

Correct option A