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问题 选择题
下列集合A到集合B的对应f是映射的共有几个（　　）
①A={-1，0，1}，B={-1，0，1}，f：x→y=x2；
②A={0，1}，B={-1，0，1}，f：x→y=
x
；
③A=R，B=R，f：x→y=
1
x
；
④A={x|x是衡水中学的班级}，B={x|x是衡水中学的学生}，对应关系f：每一个班级都对应班里的学生．
A．1B．2C．3D．4
答案

根据映射的概念：对于集合A中的每一个元素在集合B中都有唯一的元素与它对应，是映射．

考察①②③④四个集合A到集合B的对应f：

对于①、②，对于集合A中的每一个元素在集合B中都有唯一的元素与它对应，它们都是映射；

对于选项③，集合A中的元素0在集合B中没有元素对应，不是映射；

对于选项④，由于衡水中学的学生可以在衡水中学的不同的班级，故集合B中的元素可能在集合A中有几个元素对应，不是映射；

∴是映射的共有2个．

故选B．

单项选择题

对人体危害最大的颗粒污染物是（）。

A．尘粒

B．落尘

C．飘尘

D．烟尘
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单项选择题

President George W. Bush


布什总统


George W. Bush is the 43rd President of the United States. He was sworn into office on January 20, 2001, re-elected on November 2, 2004, and sworn in for a second term on January 20, 2005. Prior to his Presidency, President Bush served for 6 years as the 46th Governor of the State of Texas, where he earned a reputation for bipartisanship and as a compassionate conservative who shaped public policy based on the principles of limited government, personal responsibility, p families, and local control.
President Bush was born on July 6, 1946, in New Haven, Connecticut, and grew up in Midland and Houston, Texas. He received a bachelor’s degree in history from Yale University in 1968, and then served as an F-102 fighter pilot in the Texas Air National GuarD．President Bush received a Master of Business Administration from Harvard Business School in 1975. Following graduation, he moved back to Midland and began a career in the energy business. After working on his father’s successful 1988 Presidential campaign, President Bush assembled the group of partners who purchased the Texas Rangers baseball franchise in 1989.On November 8, 1994, President Bush was elected Governor of Texas. He became the first Governor in Texas history to be elected to consecutive 4-year terms when he was re-elected on November 3,1998.
Since becoming President of the United States in 2001, President Bush has worked with the Congress to create an ownership society and build a future of security, prosperity, and opportunity for all Americans. He signed into law tax relief that helps workers keep more of their hard-earned money, as well as the most comprehensive education reforms in a generation, the No Child Left Behind Act of 2001. This legislation is ushering in a new era of accountability, flexibility, local control, and more choices for parents, affirming our Nation’s fundamental belief in the promise of every chilD．President Bush has also worked to improve healthcare and modernize Medicare, providing the first-ever prescription drug benefit for seniors; increase homeownership, especially among minorities; conserve our environment; and increase military strength, pay, and benefits. Because President Bush believes the strength of America lies in the hearts and souls of our citizens, he has supported programs that encourage individuals to help their neighbors in need．
On the morning of September 11,2001, terrorists attacked our Nation. Since then, Preaident Bush has taken unprecedented steps to protect our homeland and create a world free from terror. He is grateful for the service and sacrifice of our brave men and women in uniform and their families. The President is confident that by helping build free and prosperous societies, our Nation and our friends and allies will succeed in making America more secure and the world more peaceful.
President Bush is married to Laura Welch Bush, a former teacher and librarian, and they have twin daughters, Barbara and JennA．The Bush family also includes two dogs, Barney and Miss Beazley, and a cat, Willie.

George W. Bush earned a reputation for______.

A．involving two political parties in his administration
B．representing two political parties
C．working for the interests of two political parties
D．supporting two political parties
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