如图，在四边形ABCD中，∠BAC=90°，E是BC的中点，AD∥BC，AE∥DC，EF⊥CD于点F． （1）求证：四边形AECD是菱形； （2）若AB=6，BC=10，求EF的长．
如果我们用“♀”、“♂”来定义新运算：对于任意实数a，b，都有a♀b= a，a♂b= b，例如3♀2=3，3♂2=2。则（人♀民）♀（中♂学）=___________________。
As we have known from the map of the world, this is ________. A. twice as large as that island B. twice as larger as that island C. as twice large as that one
在当代资本主义国家中，英国是典型的议会制君主立宪制政体，法国是典型的民主共和制中的半总统半议会制政体。从政体结构看，两国存在明显的差
单项选择。 We are going to have a class party tomorrow afternoon. ______ , Li Ming won’t be able to take part in it, he is ill in hospital. A.Fortunately B.Luckily C.Sorry
甲、乙两图分别是某市2005年1％人口抽样调查的户籍人口和流动人口金字塔示意图。该市的平均期望寿命已提高到78岁。完成问题。 与户籍人口相比（
李克强担任总理后，面对地方债隐现危机、贸易壁垒增加、热钱出逃、银行钱荒等严峻考验，在他的“新政”中，挤水分、调结构、简政放权、布局城
Being young means having all kinds of possibilities, so you should challenge your limits and go ______ your boundaries. A. beyond B. for
