下列对传统民居的叙述中，符合傣家竹楼的是（　　）

古代雅典城邦的公民由男性构成，准确地说是(   )

为确保信息安全，信息需加密传输，发送方由明文→密文（加密），接收方由密文→明文（解密），已知加密规则如图所示，例如，明文1，2，3，4对应密文5，7，18，16．当接收方收到密文14，9，23，28时，则解密得到的明文为____

阅读下面短文, 按照句子结构的语法性和上下文连贯的要求, 在空格处填入一个适当的 词或使用括号中词语的正确形式填空。

     One day a man put ____ ad in most of the newspapers in England. He said that he was a young man with millions of ____ (pound) and great knowledge. He'd like to find a girl to be his wife and the girl must be like the one in the books ____ (write) by Somerset Maugham. Thousands of parents and young girls knew about the ad at once. Parents all went to the ____ (bookshop) to look for Somerset Maugham's books. They ____ (buy) those books for their daughters ____ presents. Girls tried to get those books to read although they weren't interested in ____ (read). They wanted to know what kind of person the rich man wished for. Before long all the books of Maugham were ____ (sell) out and the writer ____ (be) known all over ____ country. Who was the rich man? It was Somerset Maugham who put the ad in the newspapers! The ad saved his books and it made him famous too!

第1个等式：a₁= $\frac{1}{1+\sqrt{2}}$ = $\sqrt{2}$ ﹣1，

第2个等式：a₂= $\frac{1}{\sqrt{2}+\sqrt{3}}$ = $\sqrt{3}$ ﹣ $\sqrt{2}$ ，

第3个等式：a₃= $\frac{1}{\sqrt{3}+2}$ =2﹣ $\sqrt{3}$ ，

第4个等式：a₄= $\frac{1}{2+\sqrt{5}}$ = $\sqrt{5}$ ﹣2，

按上述规律，回答以下问题：