A:40°
B:50°
C:90°
D:140°
They have gone to Beijing for a meeting. They will be back ________.
如图,AB切⊙O于点B,OA=23,∠BAO=60°,弦BC∥OA,则的长为 ____ (结果保留π).
下列对“孔子学院”标志的理解,不恰当的一项是( )