(i) For ∠D + ∠B = 180°, quadrilateral ABCD may or may not be a parallelogram. Along with this condition, the following conditions should also be fulfilled.

The sum of the measures of adjacent angles should be 180º. Opposite angles should also be of same measures.

(ii) No. Opposite sides AD and BC are of different lengths.

(iii) No. Opposite angles A and C have different measures.