题目

       Every year, the ancient Town of Fenghuang,  41  of China’s most well-known ancient towns, is visited by a large number of people from all over the world.  42  (fortunate), it was under water as heavy rain hit the centre of the country,  43  tens of thousands of people leaving from the area. Heavy rain and floods lasted for the past few days. Waters in the nearby river called the Tuojiang River rose by almost one meter above warning level,  44   (cause) heavy rainstorms. More than 120,000 local people and tourists have been helped to leave there because of the te 已知y＝f(x)在定义域(－1，1)上是减函数，且f(1－a)＜f(3a－1)，求a的取值范围．