齐桓公称霸、商鞅变法等历史现象反映的时代特征是（    ）

2016年11月，新西兰强震发生后，一条“满天都是中国承包的救援机，外国人看呆了”的消息在网络上流传，引发无数网友点赞。第一时间启动应急处置机制、针对中国留学生及游客及时排查、制定有效救助方案、发布安全预警……我国的一系列应急举措表明（    ）

①我国尊重和保障人权

②管辖权是主权国家的基本权利

③和平共处五项原则是我国对外关系的基本准则

④维护我国主权、安全和发展利益是我国外交政策的宗旨

Hi, everybody!
    Welcome to our newly-opened Richards Cinema Bookstore!
    Now let me introduce to you some of the new film books in our store.
Are you Chinese film fans? OK, here comes the latest 25 New Takes about Chinese films. It is a collection of 25 fresh readings of different Chinese films from the 1930s to the present. In recent years, Chinese films are very popular in the States, such as Crouching Tiger and Hidden Dragon, Hero, and Flowers of Shanghai.
    Do you like French films? Well, here is The French Cinema Book. It covers French films from the 1890s to the beginning of the 21st century. It is written for all lovers of French cinema: students and teachers, specialists and fans, and so on.
    Maybe you are Indian film fans and star-chasers. Then here is Encyclopedia (百科全书) of Indian Cinema. The book is a complete introduction to all the best Indian films. It also offers a full list of names of the famous and successful film stars in the past ten years. You know, the Indian film industry is the largest in the world after our Hollywood.
    If you like British films, we have The British Cinema Book. It is a good review of British cinema. This book contains a good many nice pictures.
    In our bookstore, you can also find books about Mexican, Japanese, Australian, German and Italian films.
Well, please help yourselves to some coffee or tea, and have a good time here!

动物细胞培养的特点是（    ）

①细胞贴壁    ②有丝分裂     ③分散生长     ④接触抑制

⑤减数分裂    ⑥传代培养的细胞一般传至十代后就不易传下去了

已知 $a+b=4$ ， $ab=1$ ，则 $a^2+b^2$ 的值是____