Someone says, "____" But I think time is even more important than money. Why? Because when money is spent, we can get it back. However, when time is gone, it'll never return. ________

    It goes without saying that the time is usually limited (有限的). Even a second is very important. ____But it is a pity that there are a lot of people who do not know the importance of the time. They spend their limited time smoking, drinking and playing. ____  

    In a word, we should save time. ____ Remember we have no time to lose.

直三棱柱ABC﹣A₁B₁C₁ 中，AA₁=AB=AC=1，E，F分别是CC₁、BC 的中点，AE⊥A₁B₁，D为棱A₁B₁上的点．

（1）证明：DF⊥AE；

（2）是否存在一点D，使得平面DEF与平面ABC所成锐二面角的余弦值为$\frac{\sqrt{14}}{14}$？若存在，说明点D的位置，若不存在，说明理由．

高三学生阳阳沉迷网络游戏。为了能经常去网吧，他多次手持凶器抢劫同学财物。人民法院认定阳阳犯了抢劫罪，依据刑法判处有期徒刑。根据违反的法律，阳阳的行为属于（    ）