题目

如图⊙O的直径垂直于弦，垂足是，，，的长为（ ）A. B.4 C. D.8 答案：【答案】C【解析】∵直径AB垂直于弦CD，∴CE=DE=CD，∵∠A=22.5°，∴∠BOC=45°，∴OE=CE，设OE=CE=x，∵OC=4，∴x2+x2=16，解得：x=2，即：CE=2，∴CD=4，故选C．用括号内所给单词的适当形式填空【1】Don't touch the dog!It's ________ (danger).【2】Lily,why don't we ________ (sing)the song in English?【3】Someone heard you________ (talk)to a girl at that time.【4】We can't allow the students ________ (take)mobile phones to school.【5】It's going to rain.Let's________ (not play)football.