如图是我国古代数学家杨辉最早发现的，称为“杨辉三角”．它的发现比西方要早五百年左右，由此可见我国古代数学的成就是非常值得中华民族自豪的！“杨辉三角”中有许多规律，如它的每一行的数字正好对应了（a+b）ⁿ（n为非负整数）的展开式中a按次数从大到小排列的项的系数．例如，（a+b）²=a²+2ab+b²展开式中的系数1、2、1恰好对应图中第三行的数字；再如，（a+b）³=a³+3a²b+3ab²+b³展开式中的系数1、3、3、1恰好对应图中第四行的数字．请认真观察此图，写出（a+b）⁴的展开式，（a+b）⁴=____．

下列关于俄罗斯的叙述正确的是（　　）

根据短文内容选择正确答案.

    Big Ben is not the name of a man. It's the name of a big clock in London. This clock has four faces. So, no matter(无论)where you stand, you can read the time on the face of Big Ben. Each face is the size of a bus. The hands are about four metres long. If you go to London, you may want to visit the Houses of Parliament(英国国会大厦). In that place you will find Big Ben sits at the top of the clock tower in the Houses of Parliament. You will probably hear it and see it. The big clock makes such a loud noise. It goes every quarter of an hour. Big Ben has been the most famous symbol(标志)of  London

下图为肺泡内的气体交换示意图。下列相关叙述不正确的是  (  )

This composition is quite good _________ some spelling mistakes.