一支两端开口的玻璃管，下端附一塑料薄片，竖直浸入水中20厘米深处，如果在管中缓慢注入某种液体，当该液面超出水面5厘米时，薄片刚好落下，该液体的密度是多大？

我国“十二五”规化对“低碳经济”给予政策支持，实现“低碳经济”的一种策略是节能．下列制备氢气的方法最节能的是（　　）

设$x\in 0,2\mathrm{\pi }$,且$\sqrt{1-\sin 2x}=\sin x-\cos x$，则（   ）

现代旅游的最主要目的是（   ）

根据材料完成下列各题。

Beethoven
Born in 1770 in Germany
A  musician (音乐家)
Died in 1827

Florence Nightingale
Born in Italy on May 12th, 1820
An English nurse
Died in 1910

Bill Gates
Born in I955 in the USA
Wrote Business @ the Speed of Thought
Owns Microsoft

Thomas Edison
Born in 1847 in the USA
Made over 1,000 inventions (发明)
Died in 1931

Yao Ming
Born on September 12th, 1980 in Shanghai, China
A basketball player
Played for the Houston Rockets, the USA