D = {x : x is a prime number which is divisor of 60}
The divisors of 60 are :
1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60

∴ x =  prime divisor of 60 = 2, 3, 5
Hence roster form of D is {2, 3, 5}