－$\frac{1}{2}$的倒数是(   )

7月15日，庆祝建党90周年重点献礼影片《郭明义》在全国公映，很多对这部电影期待已久的观众终于一饱眼福。郭明义是鞍钢矿业公司齐大山铁矿采场公路管理员。他在家庭生活并不富裕的情况下，累计为“希望工程”捐款10余万元，先后资助180多名特困生。20多年来，他积极参加无偿献血，累计无偿献血6万多毫升，相当于自身全部血量的10倍。郭明义的事迹说明(     )
①“我为人人”是以“人人为我”为前提的       
②热心公益事业是公民应当积极履行的社会责任
③社会成员之间的相互关爱有助于社会的和谐发展 
④义务献血纯属个人行为，没有必要在全社会提倡 

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