阅读理解

    US President Barack Obama visited the Badaling section of the Great Wall in Beijing on Nov. 18th, 2009. The Great Wall was the second sightseeing program for Obama during his visit to China.

    Built originally as the biggest defense work in ancient China, the Great Wall today has become one of the must-see places for visiting foreign leaders to the country in the past sixty years.

    “ I'm inspired by the majesty(雄伟壮观) of the Great Wall and grateful for the warmth of the Chinese people,” Obama said after his half-hour tour.

    “It's magical,” Obama said when walking along the Great Wall, “it reminds you of the sweep of history and our time here on earth is not that long. We better make the best of it.”

    “I brought back the admiration(钦佩) for the Chinese civilization(文明), I bring here the greetings of American people.” Obama said when climbing a watchtower to enjoy a distant view at the Badaling section of the Great Wall.

    Obama is the fifth US president to visit the Great Wall. Richard Nixon visited the Great Wall in 1972, Ronald Reagan in 1984 and Bill Clinton in 1998, In 2002, former US President George W. Bush and his wife Laura toured the same sections Obama did.

已知tanα=2，则tan2α的值为____ 

生产方式：魏晋以来，内迁的各族人民向汉族人民学习农业技艺，逐渐将原来从事____生产的习惯转变为从事____生产。而汉族人民向北方各族人民学习畜牧经验，又学习和接受他们的____、____、____等，融入汉族的生活中。

政治：十六国北朝政权的统治者，与汉族士人合作，沿袭中原地区原有的统治方式，实行____制度。

文化：北魏孝文帝改革后，____成为北方主要的通用语言。西北民族的____、____等也受到汉族人民的喜爱。

民族心理：“胡”“汉”观念逐渐淡薄，民族之间的隔阂与偏见逐渐减少。

民族关系：这一时期的民族关系，有时矛盾激化，甚至发生战争，但在总体上，民族隔阂趋于____，民族关系趋于____。北朝后期，我国北方出现了各民族的大交融。

历史意义：北方地区民族的交往、交流与交融，为中华民族的发展注入新的活力，并为____时期多民族国家的繁荣与发展奠定了基础。