题目

An audience of patients with Alzheimer’s(老年痴呆症) disease listens with concentrated attention as a young woman sings the French song “Beau Soir”. Despite his failing mind, one of the men in the crowd, Les Dean, translates the words into English for a friend.Dean, 76, once taught music at Chicago’s Senn High School, invented and sold his own music education system and sang with the Chicago Symphony Chorus. Now, like many patients with Alzheimer’s, he is, to some extent, lost in the past, a stranger to the present. But when the music plays, he smiles and is transported to a pla如图，在下列五个关系：①AB∥CD，②AD=BC，③∠A=∠C，④∠B=∠D，⑤∠B+∠C=180°中，选出两个关系作为条件，可以推出四边形ABCD是平行四边形，并以平行四边形定义作为依据予以证明．（写出一种即可）已知：在四边形ABCD中，________，________．求证：四边形ABCD是平行四边形．