-----______ there any living things on other planets ?
-----I have no ideas. Maybe we can know more about that in the future.
A:Is
B:Are
C:Has
D:Have
如图是一个古代车轮的碎片,小明为求其外圆半径,连接外圆上的两点A、B,并使AB与车轮内圆相切于点D,半径为OC⊥AB交外圆于点C.测得CD=10cm,AB=60cm,则这个车轮的外圆半径是 ____.