有一串数$\frac{1}{1}$,$\frac{1}{2}$,$\frac{2}{2}$,$\frac{1}{2}$,$\frac{1}{3}$,$\frac{2}{3}$,$\frac{3}{3}$,$\frac{2}{3}$,$\frac{1}{3}$，…这串数从左开始数，第____ 个数是$\frac{11}{11}$．

依次填入下面一段文字横线处的语句，衔接最恰当的一组是（   ）（3分）
上海世博会的组织者______， _______， _______， _______， _______， _______。目前已经有170多个国家和国际组织确认参展网上世博会。
①并使之成为世界第一个网上世博会 ②让互联网把上海世博会变成“永不落幕 的世博会” ③开创性地推出了“网上中国 2010 年上海世博会” ④充分利用互联网的独特优势 ⑤在举办实体世博会的同时 ⑥实现实体世博会和网上世博会的有机联动

用所给动词的正确时态、语态填空
⑴Be quiet, please ! The baby____ (sleep).
⑵—What does Frank often do at weekends?
—He often____ (go) to the cinema with his parents.
⑶Andy ____ (argue) with his brother when I went to see him yesterday.
⑷She ____ (be) to her hometown several times.
⑸____ (play) computer games too much is bad for your eyes.
⑹Lucy tried ____(not make) too many mistakes in the exam.
⑺He ____  to us as soon as he gets there. (write)
⑻By the time I got outside, the bus____ (leave).
⑼I'm sure I ____  her four years ago. (see)
⑽In summer,  Miss Xia would rather ____  (stay) at home than go out.

△ABC中，∠A=30°，∠B=45°，AC=4，求AB的长？

2015年5月底，美国发布了最新的SR-72高超音速飞行器设想图，如图所示，飞行器体表涂敷最新型材料，具有雷达隐形功能，但不具备红外隐形功能.

①该飞行器具有雷达隐形功能，是因为体表形状及材料能有效减弱它对____的反射.

②不具备红外隐形功能，是因为高速飞行时体表与空气摩擦将____能转化为____能，使飞行器表面温度升高的缘故.