题目

Why not ________ the new word in a dictionary if you don't know it? A．look up  B．look at  C．look for  D．look like 答案：A 点拨：考查固定短语。分析句意应是在词典中查找。look up 意为“查找”。设实数x，y满足条件则z=2x-y的最大值是    ．