题目

Su Hua is studying at Cambridge, UK. She has bought a bicycle and is worried about security（安全）. Her friend, Kate, found this article and sent it to her. Introduction A lot of crime isagainst bicycles. About 150,000 bicycles are stolen every year and most arenever found. You can prevent this happening by following a few careful steps. Basic Security Do not leave yourbicycle in out-of-the-way places. Always lock your bicycle when you leave.Secure it to lampposts or trees. Take off smaller parts and take them withyou, for example lights and saddles（车座）. Locks Get a good lock.The用频率为v的光照射某金属表面时，逸出的光电子的最大初动能为EK，若改用频率为3v的光照射该金属，则逸出光电子的最大初动能为