Mr. John plays a game with his two smart students.  He says: "I have a $2-$digit prime number. But I tell Andy only the ones digit and tell Fiona only the tens digit."  A few moments later, Andy says: "I don\textquotesingle t know what the number is, neither do you."  Fiona says: "I didn\textquotesingle t know what the number was before, but now I know it."  What is the ones digit of the prime number? 
选项为:A:$$1$$  B:$$2$$  C:$$3$$  D:$$5$$  E:$$7$$  请回答其中一个选项.