A:I want to drive a car.
B:I want to be a doctor.
C:I want to sleep.
如图,⊙O的弦AB垂直半径OC于点D,∠CBA=30°,OC=3 3 cm,则弦AB的长为( )
下列属于我国地势第一、第二级阶梯分界线的是( )
手掌宽大约为____~____厘米