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问题 选择题

已知圆O的弦AB被OC分成3cm与2cm的两段，点C为弦AB上的一点，若OC=2.5cm，则圆O直径为（　　）

A．4cm

B．5cm

C．6cm

D．7cm

答案

过点O作OD⊥AB于点D，连接OA，

∵圆O的弦AB被OC分成3cm与2cm的两段，

∴AB=2+3=5（cm），

∴AD=BD=

AB
2
=2.5（cm），

∴CD=AD-AC=0.5（cm），

在Rt△OCD中，OD=

OC2-CD2
=
6
，

在Rt△AOD中，OA=

AD2+OD2
=
7
2
（cm），

∴⊙O的直径为：7cm．

故选D．

填空题

Here is my idea about how a friend is like. Firstly, 61.______a friend is someone you can share your secrets. If you 62.______tell him a secret, never will he talks about it with anybody 63.______else. Besides, a friend is always good listener when you 64.______need one. After hear your sad stories, he will say some 65.______words that is nice and warm. Still, your happiness makes 66.______him happily, too. What’s more, a good friend is willing to 67.______offer the help to which you need, or can at least give you 68.______some advices. In a word, friends are those you like and 69.______trust, and you will enjoy every minute that you spent with 70.______them.

63().
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