A:____
B: I'm fine, thanks. And you?
A: I'm OK.____?
B: It's a book.
A:____?
B: It's red.
B: Yes. B-O-O-K , book .
A:____.
B: You are welcome.
在矩形ABCD中,∠B的角平分线BE与AD交于点E,∠BED的角平分线EF与DC交于点F,若AB=9,DF=2FC,则BC=____(结果保留根号)
动画片的配音常用慢录快放的方式,把成年人的声音变成了小孩的声音,这样做能够使声音( )