题目

 You've decided on getting a goldfish? Great!    16    Use the tips in this article to determine which fish is right for you and how to keep it healthy. Get your tank.  When kept in healthy conditions, goldfish can grow to be anywhere from five to ten inches long, even if they are half an inch when you buy them.    17    If not, you will have to continue buying larger tanks throughout the fish's lifetime.  18           There are many varieties of fish out there; Comets, Fantails, Black Moors, Pearlscales, Orandas, and hundreds more, ranging in price from thirtee如图，下列四个关系：①AD∥BC，②AB=CD，③∠A=∠C，④∠B+∠C=180°，选出其中的两个关系作为命题的题设，命题的结论：四边形ABCD是平行四边形，请写一个真命题和一个假命题．你写的真命题是：已知：在四边形ABCD中，______，______；求证：四边形ABCD是平行四边形．证明：______．你写的假命题是：题设：______；结论：四边形ABCD是平行四边形，你认为它是假命题的理由是：______．