A:在近日点时速度快、远日点时慢
B:在远日点时速度快,近日点时慢
C:角速度不变,线速度时大时小
D:线速度不变,角速度时大时小
—What is Lucy doing now? —She _____ a book.
如图,AB是⊙O的直径,D、C在⊙O上,AD∥OC,∠DAB=60°,连接AC,则∠DAC等于( )