材料一：三国和两晋时期，北方的匈奴、羯、氐、羌、鲜卑等少数民族开始内迁到黄河流域……各民族纷纷建立自己的政权……他们彼此征战，人民被屠杀，牛马被掠夺，城市化为废墟，田地大量荒芜，为躲避战乱，大批北方民众纷纷渡江南下，形成第三次南迁的浪潮。

材料二：魏晋以来，内迁的各族与当地的汉人错居杂处，开始过定居生活，他们不断向汉族人民学习，……民族隔阂不断消解，民族关系趋于和缓，到北朝后期。我国北方出现了各民族的大交融。

——节选自《人教版七年级教材》

材料三：三国鼎立时期，无论魏、蜀、吴都在局部地区实现了统一，这种局部统一较之东汉末年众多军阀割据混战的状况前进了一步，也为后来的全国统一准备了条件。各国都重视发展生产，整顿政治，增强国力，促进了局部地区经济的恢复和发展。魏、蜀、吴三国还重视处理与少数民族的关系，进一步促进了民族大融合。

化简：

（1）（2a+3b）（3a﹣2b）﹣$\frac{1}{2}$（3a+2b）²﹣a（$\frac{3}{2}$a﹣b）；

（2）$\frac{4-a}{a}$÷（$\frac{a+2}{a^2-2a}$﹣$\frac{a-1}{a^2-4a+4}$

根据短文理解，选择正确答案。

Marco Polo

    Marco Polo was born in Italy in 1254. A traveller and businessman, he was one of the first Europeans to travel across Asia and into China. His journey lasted 24 years.

    He set out, aged 17, with his father Nicolo and his uncle Maffeo on their great journey to China. They sailed south from Venice, Italy and stopped off in the Middle East. They ofen carried on overland to Persia (now Iran), through the Pamir Mountains and the Gobi Desert before they got to Beijing, China.At that time, China was more advanced than Europe. They already had paper, so large numbers of books were available. They also used paper money in many parts of the country.

    After he got back to Italy, Marco Polo talked about his experiences in China, and he wrote a book describing the riches of Asia. His book was the first western record of porcelain(瓷器), coal, gunpowder, printing and silk.Unfortunately, not many people believed Polo's stories and he became known as “the man of a million lies”. He died in 1324.

Jacques Cousteau

    Jacques Cousteau was a French undersea explorer, environmentalist and inventor. He was born in France in 1910. When he was young, he was attracted by the sea, machines and filmmaking. In the French navy, Cousteau began exploring underwater and worked on a special breathing machine which allowed divers to stay underwater for several hours. This gave them time to really look around under the ocean. In 1948, Cousteau began travelling the world's oceans in his research ship Calypso.Cousteau produced many films and books about his underwater experiences, including the TV series The Underwater World of Jacques Cousteau, which introduced the public to the world of sharks, whales, dolphins and treasure.

    Cousteau started the Cousteau Society to protect ocean life. In 1989, he received a great honour: he was made a member of the French Academy. Finally, after a long and varied life, Cousteau died on 25^th June, 1997.