Unit 3   Science and nature
                              能力提升题组训练     (A)
Ⅰ . 阅读理解
   Many years ago,people      relied  on the sun,the moon and stars to find their    way around.Later,the   compass
was introduced.And now,we have satnav (         卫星导航 ) systems to guide us.A satnav system uses groups of
satellites to show the user      ’s location. They send information to a receiver,such as a smart phone,to
show us where we are.
   The earliest    built  satnav system is the Global Positioning ...