根据短文内容，完成下列小题。

    The story is about a young student. She worked very hard at her lessons. She worked so hard that she became ill. She couldn't go to sleep at night. When she got up the next morning, she felt very tired.

    So she went to see a doctor. Hearing the student's words, the doctor said, "You are too stressed out. You must eat more food like vegetables and tofu. Besides you can try to count(数) numbers when you are lying in bed. By the time you reach one thousand, you will be asleep. I'm sure of it."

    The next day, the student came to see the doctor again. "Well," said the doctor, "how are you feeling today?"

    The student still looked tired. "Yes," she said, "I tried to count one, two, three, four... up to one thousand. But when I reached five hundred and sixty, I feel sleepy. I had to get up and drink some coffee so that I could go on counting up to one thousand. But then I still couldn't be asleep."

20世纪50年代，中国在接见印度代表团时首次提出，后来成为处理国与国关系的基本准则是（   ）

（Ⅰ）若f（x）在 $(-\infty ,\frac{1}{2}$ 是减函数，在 $\frac{1}{2},+\infty )$ 是增函数，求实数a的值；

（Ⅱ）求实数a的取值范围，使f（x）在区间﹣5，5上是单调函数，并指出相应的单调性．