题目

Since there is abundant food in the sea, it is understandable that some of the creatures that   evolved on land __________ to the sea. A. would have returned              B. could have returned C. might have returned              D. should have returned 答案：D 如图(1)，Rt△ABC中，∠ACB＝－90°，CD⊥AB，垂足为D．AF平分∠CAB，交CD于点E，交CB于点F (1)求证：CE＝CF． (2)将图(1)中的△ADE沿AB向右平移到△的位置，使点落在BC边上，其它条件不变，如图(2)所示．试猜想：与CF有怎样的数量关系？请证明你的结论．