Is ABCD a cyclic quadrilateral?
I. Points A, B, C and D lie on a circle.
II.
∠B + ∠D = 180°.
(a) if the given question can be answered by any one of the statements but not the other;
(b) if the given question can be answered by using either statement alone;
(c) if the given question can be answered by using both the statements together but cannot be answered by using either statement;
(d) if the given question cannot be answered by using both the statements together.