______I have one healthy habit, ______I’m not very healthy. A. Although , but B. Although, / C. Although ,so D. but , / 答案:B如图,AB是⊙O的直径,C、D是⊙O上一点,∠CDB=20°,过点C作⊙O的切线交AB的延长线于点E,则∠E等于( )A. 40° B. 50° C. 60° D. 70°
B
【解析】试题分析:连接OC,如图所示:
∵圆心角∠BOC与圆周角∠CDB都对,
∴∠BOC=2∠CDB,又∠CDB=20°,
∴∠BOC=40°,
又∵CE为圆O的切线,
∴OC⊥CE,即∠OCE=90°,
则∠E=90°﹣40°=50°.
故选B