题目

How northern Europeans beat the winter blues Ask a child from northern Europe to draw two pictures—one on a rainy day and a second in the sunshine—and this is what you will get: in the first, as raindrops fall from the top of the page, the man behind the window has an unhappy expression. When a yellow sun sends out some light from the corner, the man is smiling. Northern Europeans associate rain with sadness and sunshine with happiness. They think this is true because they are so aware of how their environment affects them. ___71___In October 2008, a group of researchers examined th已知函数， (Ⅰ)若a=2，求f（x）的定义域； (Ⅱ)若f（x）在区间(0，1]上是减函数，求实数a的取值范围。