题目

已知x∈R, sin x－cos x＝m，则m的取值范围为( ) A．－1≤m≤1                    B．－≤m≤ C．－1≤m≤                 D．－≤m≤1 答案：BWhenever he meets difficulties, he always takes a positive _________ towards them. A. mind B. attitude C. opinion  D. state