题目

They are Larry's and Becky's phone numbers.Please ________，John. A．write it down     B．write down it  C．write them down  D．write down them 答案：C在R上定义运算?：x?y=x（1-y），若不等式（x-a）?（x+a）＜1对一切实数x都成立．求实数a的取值范围．