题目

函数的定义域为，若存在闭区间，使得函数满足： ①在内是单调函数； ②在上的值域为，则称区间为的“倍值区间”． 下列函数中存在“倍值区间”的有_______ ①；            ②； ③；        ④ 答案：_①③④_ 句型转换 He went out; his TV was turning on and the door was open． He went out, ________ his TV ________　________ and the door．