题目

What does the man mean? A . The doctor won't see the woman tomorrow. B . The doctor is busy all day today. C . The doctor is busy tomorrow. 答案：B设定义在R上的函数，若关于x的方程f2（x）+af（x）+b=3有3个不同实数解x1、x2、x3，且x1＜x2＜x3，则下列说法中正确的是________①a+b=0；②x1+x3＞2x2；③x1+x3=5；④．x12+x22+x32=14．