—  Look! The black clouds are gathering, which indicates that it __________ rain soon.

— Yes, black clouds are the _________ of the rain. [ ]

A. is going to; signal      

B. will; mark

C. is gong to; sign

D. is to; sign

桌上摆着9 张卡片，上面分别写着1 ～9 这九个数，任意摸一张，摸到单数的可能性是(    ) ，摸到双数的可能性是(    ) 。