London is one of the most popular sites in the world for tourists to visit.If you are planning a trip to London in the future,you're lucky.There are a variety of attractions for you to enjoy.

    One of the most popular tourist attractions in London is the Tower of London.Founded more than 900 years ago, the Tower of London is one of the world's most famous towers and has changed a lot.Here,you can also find the seven ravens（乌鸦）which live in the Tower.There is a story that says: If there are no ravens in the Tower, the Tower and the kingdom will fall.There are also lots of tours,exhibits.and special events that you can enjoy throughout the year.

    Another popular place to visit is Westminster Abbey.It was set up in 1065 by Edward the Confessor.Visitors to Westminster Abbey can enjoy its beautiful special Gothic architecture（哥特式建筑）.There are also lots of memorials of Kings and Queens to enjoy.Excellent transportation is available here by bus or tube from many locations in London.

    Buckingham Palace is another place with a rich history to discover.It's the official London residence（住处）of Queen ElizabethⅡ.During August and September,you can visit the State Rooms and see the Changing of the Guards.The Queen's Gallery is open to the public daily.Checking the official timetable before you make sure to visit the Palace is a must,because it is not open year round.

在世界的不同地区，不同时代，社会政治制度呈现多元化的特点，但人类在政治制度上有着共同的目标。

材料一：公元前430年，希米奥30岁，他是一个普通商人家庭中的男主人。有一天，他去参加事实上的国家最高权力机关——公民大会，并在会上发言和表决，还领取了一份国家发放的工资。

材料二：

材料三：主权在实质上属于法兰西人民；所有公职人员都是受人民委任的人员，人民选举他们，也能罢免他们……为了不使财产的不平等挤掉权利的平等，宪法要求靠自己劳动生活的公民相应法律号召而在人民集会中担任公共职务时，对其所花费的时间应给予报酬。

——法罗伯斯庇尔《论代议制政府》(1793年)

某种大型商品，A，B两地都有出售，且价格相同、某地居民从两地之一购得商品后运回的费用是：每单位距离A地的运费是B地的运费的3倍，已知A，B两地距离为10千米，顾客选择A或B地购买这种商品的标准是：包括运费和价格的总费用较低，求A，B两地的售货区域的分界线的曲线形状，并指出曲线上、曲线内、曲线外的居民应如何选择购货地点

李亮同学在实验室里发现一张脱落标签的永久装片，他借助显微镜观察到如图所示的图象，该装片属于（ ）