已知函数f（x）=asinx+bcosx，其中a∈R，b∈R，如果对任意x∈R，都有f（x）≠2，那么在不等式①﹣4＜a+b＜4；②﹣4＜a﹣b＜4；③a²+b²＜2；④a²+b²＜4中，一定成立的不等式的序号是（　　）

阅读理解

     Hello! My name is John, I have a happy family. There are four people in my family. They're my father, my mother, my baby sister and I. We have a beautiful garden. There are two trees and some flowers in it. There are some apples on the tree. Do you like apples and flowers? Welcome to my home.