Correct option is A.
When di < 0 we choose east pixel and for next points increment X and no change in Y then add east pixel value to old di for new di.
When di > 0 we choose north east pixel and increment both X and Y and add value of North pixel to di.
When di = 0 we can choose any one of them to find next points to be plotted.
Hence, di < 0 is satisfied by option A.