Answer C)
Pick
B B - both ball thrown up
B W - Black ball throw away
W B - Black ball throw away
W W - both ball thrown up
So, in 4 times of throw waste of black ball 3 times and waste of white balls 1 time
So, probability ratio of Black ball with white ball =3:1
As we taking two ball in each pick ratio will be (347/2) : (278/2) ≈173:139
So, in ratio no of white ball is more as it should be
So, white ball should remain in last