完形填空（共10小题；每小题2分，满分20分）
阅读下面短文,从短文后各题所给的A、B、C三个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
Many thousands of years ago，there are no houses such as people live in today. Men sometimes made their homes____so as to be safe from their____and wild animals；the leaves of the trees would keep the rain and sun____.
In cold areas，ancient people used ___their homes in caves. It was too cold and stormy to live in trees there.
As years went on，men____more about living in comfort and safety.They___their trees and caves and built houses of different materials___mud，wood or stones.
During the last hundred years，many new building materials and new methods of building____.People now live comfortably in a variety of houses.
____design or materials are used，the buildings should be bright，airy and comfortable. Human beings need sunlight and fresh，clean air in order to remain____.
A. in trees             B．in rivers      C．on the grass
A. friends             B．neighbors     C．enemies
A. in                 B．off           C．down
A. make               B．to making    C．to make
A. saw                B．learned       C．recognized
A. came to             B．went on      C．left
A. according to          B．for example  C．such as
A. have been discovered   B．were discovered C．had discovered
A. No matter where       B．No matter what C．No matter when
A. active              B．healthy      C．happy