Correct Answer - A
For parallel composite slab
`mu"sin"theta = "constant"`
`(mu_(1)xxa)/(sqrt(a^(2) + b^(2))) = (mu_(2) xx c)/(sqrt(c^(2) + d^(2)))`
`because |hatr_(1)| =|hatr_(2)| = 1 therefore (sqrt(a^(2) + b^(2))= sqrt(c^(2) + d^(2)) = 1)`
`therefore mu_(1)a = mu_(2)c`