____What's this?
____Good afternoon.
____It's an apple.
____Yes, please.
____Would you like an apple?
____What about a pear (梨)?
____No, thanks.
如图,AB是⊙O的弦,D为半径OA的中点,过D作CD⊥OA交弦AB于点E,交⊙O于点F,且CE=CB.
(1)求证:BC是⊙O的切线;
(2)连接AF、BF,求∠ABF的度数;
(3)如果CD=15,BE=10,sinA=513,求⊙O的半径.
下列各句中,划线的成语使用恰当的一项是( )
区别CO和CO2最简便的方法是