A box contains `4` white and `3` black balls. Another box contains `3` white and `4` black balls. A die is thrown. If it exhibits a number greater than 3`, the ball is drawn from the first box. Otherwise, a ball is drawn from the second box. A ball drawn is found to be black. The probability that it has been drawn from the second box is
A. `3//7`
B. `4//7`
C. `6//17`
D. `8//17`