一个密闭不透明的盒子里有若干个白球，在不允许将球倒出来的情况下，为估计白球的个数

阅读理解

     Jeff  Keith has only one leg. When he was 12 years old ,Jeff had cancer . Doctors had to cut off most of his right

leg.

     Every day Jeff puts on an artificial(人造的) leg. The leg is plastic. With the plastic leg Jeff can ski ,ride a bicycle,

swim and play soccer. He can also run.

     Jeff made a plan with his friends who had plastic legs, too. They decided to run across America. They all wore

special T-shirts. On it was "Run ,Jeff, Run ,Jeff Keith's Run Across America."

     When he was 22 years old,Jeff  Keith ran across the United States from the east to the west. He started running

in Boston. Seven  months later ,he stopped running in Los Angeles . He ran 3200 miles. Jeff wore out 36 pairs of

running shoes and five plastic legs. Jeff stopped in cities on the way to Los Angeles. In every city people gave

Jeff money .The money was not for Jeff ,but for American Cancer Society .The Society used the money to know

more about cancer .

     On the way to Los Angeles Jeff talked to people about cancer. Jeff is disabled ,but he can do many things. He

finished college and is studying to be a lawyer .Jeff says,"People can do anything they want to do .I want people

to know that I ran not only for disabled people ,I ran for everybody."

1. Jeff's right leg was cut off  because of  the ________.

A .TB

B. an accident

C. cancer

D. hurt

2. Jeff's friends ran across America with him .They all have no ________.

A .T-shirts

B. legs

C. shoes

D. bicycles

3. The sentence "I ran for everybody " means ________.

A . he wants to get more artificial legs

B . people can do anything they want to

C . some disabled men will become lawyers

D . disabled people can also run  

若某一保险标的由法律限定，但投保人可以自由选择保险人，则该保险方式属于（）。

A．普通保险

B．强制保险

C．自愿保险

D．商业保险

美卡拉明是( )。

A．M受体阻滞药
B．N₁受体阻滞药
C．N₂受体阻滞药
D．a₁受体阻滞药
E．β受体阻滞药

支承件的作用是什么？

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