Assuming that a!=b!=c I can prove that the eqn can't have 3 real roots and hence a,b, c being real and complex roots occuring in conjugate pairs the option (b) is correct .
The proof goes as follows :
Denote the LHS by f(x) and assume that it has three real roots . Then f'(x) =0must have atleast two real roots
That is (x-a)^2 + (x-b)^2 + (x-c)^2 = 0 has atleast two real roots
but it is give that a!=b!=c , so the above eqn has no real roots at all !!
Hence it must have one real and two conjugate imaginary roots .