title: 几个单选题,要理由1.Shanghaiis______inthe 
desc: 1.Shanghai is ______ in the world.
  A.a largest cy B.one of largest cities
  C.one of the largest cityD.one of the largest cities
  2.These are _______houses.
  A.Mr Green's and Mr Wang's B.Mr Green and Mr Wang's C.Mr Green's and Mr Wangs D.Mr Greens' and Mr Wangs
  3.The computer1.Shanghai is ______ in the world.
  A.a largest cy B.one of largest cities
  C.one of the largest cityD.one of the largest cities
  2.These are _______houses.
  A.Mr Green's and Mr Wang's B.Mr Green and Mr Wang's C.Mr Green's and Mr Wangs D.Mr Greens' and Mr Wangs
  3.The computer on the desk is_____.
  A.twins B.the twin's C.the twins D.the twins'
answer: 1)D
  是世界最大的城市当中的一个,这里"最大的城市"是一个群体,复数
  2)A
  Mr Green's and Mr Wang's 
  Green先生的房子和王先生的房子.两个不同的房子
  和are, houses对应
  B是两个人共有的房子,动词和名词都要单数
  
  3)D 用名词性物主代词
  以S结尾的直接加'