题目

第一节  完形填空（共15小题，每小题2分，满分30分） 阅读下面短文，从短文后所给各题的四个选项（A、B、C、D）中选出能填入空白处的最佳选项，并在答题卡上将该项涂黑。 Paul received an expensive car from his brother as a Christmas present．On Christmas Eve Paul saw a dirty and poorly-dressed boy walking  1  his shining car．“Is this your car，Paul？”he asked． Paul told him how he got the car and the boy was  2 ．“You mean your brother gave it to you and it didn’t  3  you anything？Boy，I wish…”  he said设函数f（x）的定义域是R，对于任意实数m，n，恒有f（m+n）=f（m）•f（n），且当x＞0时，0＜f（x）＜1．（1）求证：f（0）=1，且当x＜0时，有f（x）＞1；（2）判断f（x）在R上的单调性；（3）设集合A={（x，y）|f（x2）•f（y2）＞f（1）}，B={（x，y）|f（ax-y+2）=1，a∈R}，若A∩B=∅，求a的取值范围．