Question 1: Select 1, 2,3 as the topic (condition). Because AD//BC, Angel Addo = Angel OBC. Because AOD angle and COB angle are diagonal, AOD angle = COB angle. BO=DO because AC divides BD equally. So triangle AOD and triangle COB are congruent, so AO = Co So the quadrilateral ABCD is a parallelogram, because AC is perpendicular to BD, so the quadrilateral ABCD is a diamond.

Question 2: Choose 2, 3 and 4 as questions (conditions). Because angel ·OAD = angel oder, OA=DO. Because AD//BC.

So OBC angle = Oder angle = OAD angle = OC angle, so OB=OC. BO=DO because AC divides BD equally. So OA=OD=OB=OC. So AC=BD, and because AC divides BD equally, the quadrilateral ABCD is a rectangle, so it is impossible to determine whether it is a diamond.