如图，在Rt△ABC中，∠ACB＝90°，D是AB边上的一点，以BD为直径的⊙O与边AC相切于点E，连接DE并延长，与BC的延长线交于点F．

（1）求证：DE＝FE；
（2）若BC＝9，AD＝6，求BF的长．

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根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。有两个选项为多余选项。

    The Internet has opened up a whole new online world for us to meet, chat and go where we've never been before.

    But just as in face to face communication, there are some rules of behavior that should be followed when on line. ____ Imagine how you'd feel if you were in the other person's shoes.

    For anything you're about to send: ask yourself, “Would I say this to the person's face? If the answer is no, rewrite and reread. ____

    If someone in the chat room is rude to you, your instinct (本能 ) is to fire back in the same manner. But try not to do so. ____ If it was caused by a disagreement with another member, try to fix the situation by politely discussing it. Remember to respect opinions of others in the chat room.

    ____ Offer advice when asked by newcomers, as they may not be sure what to do or how to communicate. When someone makes a mistake, whether it's a stupid question or an unnecessarily long answer, be kind about it. If it is a small mistake, you may not need to say anything. Having good manners yourself doesn't give you license to correct everyone else. ____ At the same time, if you find you are wrong, be sure to correct yourself and apologize to those you have offended.

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