题目

.  — When did they come back last night? — It was midnight ____ all of us were sleeping. A. that   B. when     C. which    D. in which 答案：B（本题分）如图，请在下列四个关系中，选出两个恰当的关系作为条件，推出四边形ABCD是平行四边形，并予以证明．（写出一种即可）关系：①AD∥BC，②AB=CD，③∠A=∠C，④∠B+∠C=180°．已知：在四边形ABCD中， ， ；求证：四边形ABCD是平行四边形．