题目

若函数f（x）=单调递增，则实数a的取值范围是（ ） A. （，3）       B. [，3）        C. （1，3）       D. （2，3） 答案：B—Excuse me, can you tell me _____?—Sorry, I don’t know. You can go to the information desk.A.that there is a train B. when the train leavesC.which train can I take D.where does the train go