如图，点D是⊙O直径CA的延长线上一点，点B在⊙O上，且AB＝AD＝AO．求证：BD是⊙O的切线；若点E是劣弧BC上一点，弦AE与BC相交于点F，且CF＝9，cos∠BFA＝，求EF的长．
As a young man, there was __________ time __________ I hated to go to school .
—I am leaving for the States tomorrow, Caroline! —______
As we all know, many Chinese words have come into English, _____ typhoon, tofu and kung fu.
If better use is _______ of your spare time, you’ll make great progress in your study.
A number of books in the library ___been stolen so that the number of them___ smaller than before.
，求EF的长．
，求EF的长．
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