Around the world more and more people are taking part in dangerous sports and activities．Of course，there have always been people who have looked for adventure--those who have climbed the highest mountains，explored（探险）unknown parts of the world or sailed in small boats across the greatest oceans．Now，however，there are people who seek（寻找）an immediate thrill（令人激动的事情）from a risky activity which may only last a few minutes or even seconds．
I?would consider bungee（蹦极）jumping to be a good example of such an aetwity．You jump?from a high place（perhaps a bridge or a hot air balloon）200 metres above the ground with an elas-tic（弹性的）rope tied to your ankles．You fall at up to 150 kilometres an hour until the rope stops you from hitting the ground．It is estimated that 2 million people around the world have now tried bungee jumping．Other activities which most people would say are as risky as bungee jumping involve（包括）jumping from tall buildings and diving into the sea from the top of high cliffs．
Why do people take part in such activities as these?Some psychologists（心理学家）suggestthat it is because life in modern societies has become safe and borin9．Not very long ago，people’s lives were constantly under threat．They had to go out and hunt for food，diseases could not easily be cured，and life was a continuous battle for survival．
Nowadays，according to many people，life offers little excitement．They live and work in?comparatively safe environments;they buy food in shops;and there are doctors and hospitals to look?after them if they become ill.The answer for some of these people is to seek danger in activities such?as bungee jumping.
In bungee jumping,you__________.
从文章第二段的描述可知答案是C项。
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
