题目

My parents didn't              when they were young．Now they are always asking me to work hard． A．have a great time                              B．go to college C．travel around the world                        D．get enough exercise 答案：B设函数数f（x）=2x+1x-1（x＜0），则f（x）（　　）A．有最大值B．有最小值C．是增函数D．是减函数