题目

There is a growing ________ among young people to continue living with their parents after college. A. tendency                             B. preference C. intention                            D. alternative 答案：A把蜡烛放在距离凸透镜50cm处，在透镜另一侧的光屏上观察到倒立、缩小的清晰像．那么凸透镜的焦距不可能是A. 5cm B. 10cm C. 20cm D. 30cm